The Power of Three (TV story)

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The Power of Three was the fourth episode of series 7 of Doctor Who.

It featured the reappearances of Brian Williams and UNIT. Kate Stewart, daughter of the Brigadier, made her first appearance in a piece of BBC-produced television. It marked Amy and Rory's return as full time companions.

Unusually, life with the Doctor is seen from the companions' point of view, although this is because Amy and Rory are "part-timers". A similar situation occurred in The Sarah Jane Adventures, where the Doctor popped up in two stories as a guest character, while Sarah Jane was living her life.


There have been many ways to invade the Earth, and the Eleventh Doctor has seen them all – or so he always thought. And then the human race wakes up one morning and discovers the world has been overrun by small cubes, which then proceed to do nothing at all. A plan is afoot, humanity is endangered – but by what and how and, above all, when? Thus begins the Year of the Slow Invasion.

For the first time in his world-saving career, the Doctor has to call upon one of the least of his virtues: patience. And the Ponds face something possibly more terrifying than any world-ending apocalypse: the Doctor is moving in!


In July, Amy and Rory return home after a trip with the Eleventh Doctor. They have been gone long enough that much of the food in their refrigerator has spoiled, their dirty laundry is pungent, and 59 messages accumulated in their answering machine. They promptly begin taking care of these problems. Lounging outside with some tea, Rory realises that they have two lives: life with the Doctor and their everyday life. Amy wonders what they should do, to which Rory says that they have to choose. However, the sound of the TARDIS arriving interrupts them; "But, not right now." they both agree.

Life with the Doctor is mad, wonderful and exciting because there's always something interesting around the corner even if, occasionally, this new discovery then tries killing you; everyday life on Earth is rather, well, dull, predictable and uninteresting. Every time that Amy and Rory go away with the Doctor, they become a part of his life; however, he has never stuck around long enough to become a part of theirs; until now.

As Amy and Rory sleep, a mysterious black cube materialises in their room. They're awoken the next morning by Rory's father, Brian, who gets them to notice that many black cubes are filling the streets. Amy and Rory are shocked. They go outside and find the Doctor examining a cube in the park right across the street; "Invasion of the small cubes. Got to admit, didn't see that one coming."

Several news reports show that the cubes are all over the world, and every specialist in the unusual and alien is trying to figure out what the cubes are. Regardless, people have started taking them home, despite the fact they could be dangerous; governments have been collecting them as well, hoping to put the cubes through tests to determine what they are and if they pose a threat. Some speculate that this could be the most clever marketing campaign ever.

In the meantime, the Doctor and his family examine the cubes in the TARDIS, which he has moved into Amy and Rory's home. Brian makes several possible guesses as to what the cubes could be, such as spaceships, bombs, hard drives and pieces of a puzzle. Impressed, the Doctor congratulates Brian on being very thorough with his theories. Instructing Brian to watch the cubes for any activity, the Doctor takes some equipment from the TARDIS, planning to turn the Ponds' kitchen into a makeshift lab.

Rory goes to dress for work, surprising the Doctor; Amy reminds him his scrubs are in the lounge. Amy asks what he thinks they're doing when not travelling with him; the Doctor retorts, "mostly kissing, I guess". Setting up his equipment, the Doctor learns Amy now writes for a travel magazine, having given up her modelling job, and that Rory works part-time at a hospital. Amy explains that she can't settle on a job as she's always waiting for him to show up; she then adds that including present day years and the time in the TARDIS, she guesses they have travelled for over a decade.

As they continue talking, a UNIT strike team breaks into the house, bringing a trouser-less Rory into the kitchen with them. Amy jokes about being envious of Rory's situation. A woman named Kate Stewart walks in and apologises for the rudeness of the UNIT soldiers; "all this muscle and they still don't know how to knock." She uses a device to X-ray the Doctor and confirms his identity; from UNIT's reports, the Doctor has two hearts and a strange dress sense. Kate goes on to explain that a spike in artron energy tipped them off to his presence. They need the Doctor's expertise to deal with alien threats they haven't dealt with. She continues, saying that they've tried destroying the cubes by several means; the cubes survived plus and minus 200 Celsius, simulated five miles of water depth, being dropped out of a helicopter at 10,000 feet, and being rolled over by their best tank. The Doctor decides that the best thing to do is observe the cubes.

After UNIT departs, the Doctor watches the cubes with Amy and Rory, but quickly becomes bored; four days and nothing has happened. Needing to be constantly busy or risk the loss of his sanity, the Doctor performs several different tasks; he paints the Ponds' fence, practices with a football, and vacuums their house. Seeing that it only took him an hour to do these things, the Doctor prepares to go off and have a few adventures to restore his sanity. He finds Brian still inside the TARDIS, watching the cubes; the Doctor points out it's been four days. Brian laughs, saying that time flies when you're alone with your thoughts. The Doctor hands him the cubes, telling him, Amy and Rory to continue monitoring them; if they need him, they know his phone number. Amy is not sure he should leave, so the Doctor reassures her by explaining that he will program the TARDIS to monitor all news channels from this day onward; if anything changes with the cubes, he will be updated immediately and return to deal with it.

As time goes on, Amy and Rory live their normal lives, taking on commitments. In October, Amy promises to be a bridesmaid at her friend Laura's future wedding, while Rory agrees to work full time at the hospital. Both tell each other what they did, finding it a bit odd as they're so used to travelling with the Doctor. In the meantime, Brian has been keeping a log; he watches a cube when he's awake and records it when he's asleep. Rory mocks him for near-religiously following the Doctor's orders, but Brian remains adamant and continues his log. At this time, the cubes have become part of everyday life, being used for multiple different tasks.

During December, Rory deals with a patient who has his foot stuck in a toilet again, while a small girl appears to be possessed by her cube. An old man is in his room, waiting to be given his medication and discharged as an orderly enters, asking if he needs anything. He says no as a second enters; the old man asks this orderly to have the other leave. Despite his protests that he doesn't need help, the orderlies try subduing him. In the middle of his struggle, he removes one of their masks, revealing their inhuman nature. As the old man screams, the little girl (who had also entered the room) looks on with an expressionless face.

During the Ponds' anniversary, 26 June Amy phones the Doctor, wondering where he is; she's left several messages. He arrives with a bouquet just as she finishes her call, telling her to collect Rory as he has a present for them. He takes Amy and Rory with him to the Savoy Hotel's opening night in 1890 as his anniversary gift to them. However, despite his promise that nothing would go wrong, they ended up having to stop Zygons, who had replaced half the staff, from trying to remove their spaceship from underneath the hotel. They continued to go on several trips, during which Amy accidentally married Henry VIII.

Eventually, the Doctor takes them back home to finish their anniversary with friends and family. Brian, noticing that Amy and Rory are wearing different clothes from before they left with the Doctor, asks him how long they've been gone. Explaining that it's been seven weeks, the Doctor is asked what happened to all his previous companions. With a look of regret, the Doctor explains that most of them have left willingly or he purposely left them behind, and very few have died. However, he promises to Brian that he will do everything he can to make sure Amy and Rory don't die while travelling with him. Admitting to Amy that he misses them, the Doctor asks if he can stay with her and Rory.

During July, exactly one year after the cubes appeared, Brian prepares to take a nap while his camera records for him; the cube spins slightly after he closes his eyes. Noticing this, he tricks it into thinking he's asleep, catching it spinning. At the Ponds' house, Rory sees a cube open on the side opposite of him. He tries to see what's inside of it, only to have the device toy with him and open on sides he can't see. Amy sees one glow and touches it, only for it to prick her hand with needles and take her pulse. Playing a tennis game on the Ponds' Wii, the Doctor sees a cube float in front of the screen; he dismisses it at first but realises the severity of what's happening. He threatens that if the ones who created it wish to harm humanity, he will defend them to his last breath; it fires a laser, forcing him to flee into the hall.

Brian arrives just as everyone meets and talks over each about what their cubes are doing. The Doctor looks back to see that his cube surfed the web and that there are news reports saying that some of the cubes have caused injuries all around the world. Rory is called in to assist with those injured in the area; Brian goes with him to offer any assistance he can. The Doctor discovers a message on his psychic paper, telling him to go to the Tower of London, which houses one of UNIT's bases. Kate explains that several of the cubes captured by them each display only one unique function; some harmful ones are spewing fire or causing mood swings, while the harmless ones do things such as playing the "Chicken Dance" in an endless loop. The Doctor sets a computer to look for the source of the signal activating the cubes.

Noticing that Kate is beginning to panic, the Doctor tells her not to despair as her dad didn't. Kate is left shocked as to how the Doctor figured out her identity; she's the daughter of his old friend, the Brigadier. He questions her as to why she dropped "Lethbridge" from her name, learning she did so to not get any favours from those in UNIT who knew the Brig. Kate explains that her dad taught her everything he could and that, in the words of his old friend, "Science leads", explaining why she took the position of Head of Scientific Research. The Doctor smiles; his old friend taught his daughter the most valuable lesson from their time working together. Suddenly, the cubes become inactive after 47 minutes. The Doctor is left confused and goes outside, complaining about the lack of ventilation underground bases have.

At the hospital, Rory sends Brian to retrieve some medical supplies he needs to treat patients. Not knowing where the supplies are, Brian asks the two "orderlies" for some help. However, they ignore him. Brian continues to ask for help, seemingly annoying them as they turn around with sedatives in hand. Brian is left shocked.

Outside the Tower, the Doctor and Amy debate the merit of travelling the way they do; Amy considers it "running away" and the Doctor considers it "running to"; he travels to see whatever the universe holds before it's gone forever. During their conversation, the Doctor realises the cubes acted out to gain attention and scan the entire planet. The power at UNIT goes out, and the cubes start a countdown from seven. The Doctor locks himself in a room with a cube, ready to confront what's inside. At zero, the cubes open but contain nothing; the Doctor is perplexed. Moments pass when around the world, people start going into cardiac arrest, with the Doctor in pain with one of his hearts failing. The program he set earlier to find the source of the cubes comes up on the screen, revealing seven different sources; the nearest being the hospital where Rory works. He and Amy leave for the hospital.

At the hospital, Rory is searching for Brian. Seeing him being wheeled into an out-of-order lift by the false orderlies, Rory follows only to find it empty. Touching the back wall in the lift, Rory finds it houses a portal. It takes him to an alien ship, which houses patients that have been kidnapped over the entire year. The two orderlies close in on him with sedatives.

The Doctor and Amy arrive at the hospital, looking for both Rory and Brian along with the source of the cubes' signal. The Doctor discovers the little girl with the active cube and reveals her to be a simple android overseeing the entire operation. The Doctor shuts her down with the sonic screwdriver, but collapses in pain as one heart is not enough to keep him alive. Amy quickly grabs a defibrillator and, despite his protests, manages to restart the Doctor's other heart. The Doctor dances with joy, thanking Amy; however, he then orders her to "never do that again." They abandon the deactivated android girl, dead in the hallway, and continue looking for the energy source.

Tracing the signal, they discover the same out-of-order lift and use the portal inside it to reach the alien ship. The Doctor explains that the ship exists outside of the universe, and they travelled through a wormhole. They find Rory unconscious and quickly wake him. The Doctor disables the orderlies while ordering Amy and Rory to return everyone that was kidnapped through the portal. The Doctor examines the monitors, discovering that seven ships are using seven portals to reach earth. A humanoid appears on the other side of the monitors.

Amy and Rory return, confused by the sight of him. The Doctor explains it's one of the Shakri, who are told of in Gallifreyan legends as, in the Doctor's words, the "pest controllers of the universe". The Shakri consider humanity to be a plague that must not spread, hence why they've chosen to start killing them; the blackouts were caused by the cubes sucking up electricity to exterminate one-third of humanity. The Doctor says that humans have done more good than harm, and he is willing to defend them regardless of what the Shakri believe.

With a smug smile, the humanoid announces another wave of cubes will be soon be unleashed on Earth, before vanishing. Amy is left confused as to what happened. The Doctor explains it was simply a hologram produced by the ship; similar to a "talking propaganda poster". Fiddling with the controls, the Doctor takes control of the cubes already on Earth; he manages to reverse the damage done by the cubes, restarting the hearts of everyone killed by the Shakri. However, as a downside, this task has created a backlash of energy that will blow up the ship. The Doctor, Amy and Rory flee to the portal, barely managing to get back to the hospital in time.

The Doctor and the Ponds set off again.

After having dinner with Amy, Rory and Brian, the Doctor prepares to take off for solo adventures again. However, Brian encourages Amy and Rory to return to being the Doctor's full-time companions; travelling with the Doctor gives them the chance to save the world and make it better. The Doctor agrees, even offering Brian a place in the TARDIS. However, Brian turns down the offer, saying that someone has to stay behind and water the plants. The Doctor and the Ponds board the TARDIS and shut the door.

Amy narrates, saying, "So that was the year of the slow invasion when the Earth got cubed, and the Doctor came to stay. It was also when we realised something the Shakri never understood. What cubed actually means. The power of three."


Uncredited cast[[edit]]


General production staff

Script department

Camera and lighting department

Art department

Costume department

Make-up and prosthetics



General post-production staff

Special and visual effects


Not every person who worked on this adventure was credited. The absence of a credit for a position doesn't necessarily mean the job wasn't required. The information above is based solely on observations of the actual end credits of the episodes as broadcast, and does not relay information from IMDB or other sources.

Uncredited crew[[edit]]

Space Digital[[edit]]


Communications technology[[edit]]


  • The Doctor uses several different magnifying glasses to examine the cubes.
  • Kate uses a handheld scanner to examine the Doctor's double hearts.


Energy and radiation[[edit]]

Foods and beverages[[edit]]

Game consoles[[edit]]

  • Though no gameplay footage is shown, sound effects indicate that the Doctor plays the "tennis" mode in Wii Sports on the Nintendo Wii.


  • Amy accidentally marries Henry VIII.
  • While playing virtual tennis, the Doctor mentions the tennis player Fred Perry and a pair of shorts he had borrowed from him.
  • The real physicist Brian Cox plays himself as he is interviewed on the news for an opinion about the cubes.


  • The song "Merry Xmas Everybody" by the rock band Slade is briefly heard in the hospital.
  • One of the cubes plays the "Chicken Dance" song on an endless loop.
  • The song "Titanium" plays at the party Amy attends.
  • "Don't Falter" by Mint Royale plays during the garden party.

Popular culture[[edit]]


  • There were Zygon duplicates at the Savoy when Amy, the Doctor and Rory visit, and the Doctor claims there is a Zygon spaceship beneath the hotel.



  • Chris Chibnall's brief from Steven Moffat was to "live with the Doctor — The Man Who Came to Dinner, Doctor Who style."
  • The plot of the episode is similar to, if not the same as, a game called Surviving Mars. Even Brian's line: "What if they're bombs, billions of tiny bombs? Or transport capsules maybe with a mini robot inside? Or deadly hard drives? Or alien eggs? Or messages needing decoding? Or they're all part of a bigger whole, jigsaw puzzles that need fitting together?" can be found in this game.

Story notes[[edit]]

The unique logo for The Power of Three.
  • For this episode, the Doctor Who logo's texture resembles the Shakri cubes featured prominently in the episode. Also, the shade of red in the time vortex appears to be more crimson, rather than orange, with the lightning strikes causing an additional effect of electrical surges spreading out from the tips of the bolts. The vortex also turns purple with the sharpness seriously decreasing when the title appears.
  • The working title for this episode was Cubed.[4]
  • The character of Kate was introduced in the 1995 made-for-video independent production HOMEVID: Downtime.
  • Though not made clear in the episode, the scene in Henry VIII's bedroom was intended to show the TARDIS trio returning to get Rory's mobile phone charger after Rory had left it behind before TV: A Town Called Mercy [+]Loading...["A Town Called Mercy (TV story)"]. (TCH 71)
  • Chris Chibnall is the first non-showrunning writer in the revived series to write multiple stories within the same season, having previously written TV: Dinosaurs on a Spaceship [+]Loading...["Dinosaurs on a Spaceship (TV story)"]. He would later become the showrunner in 2018.
  • This is the last appearance of the Eleventh Doctor's blue bow tie, which he wears along with his more commonly worn red one to reflect the length of time passed in this story.
  • Chris Chibnall was inspired by the story of the MSC Napoli, a 2007 shipwreck along the Devon coast near his home, when people showed up in droves to claim cargo which had washed up on the shore. This led to the notion of the general public collecting alien items which initially appeared to be innocuous, but which would ultimately be revealed to have a more sinister purpose.
  • Matt Smith put disgust into the Doctor's remark concerning Twitter in the episode, reflecting his real-life decision to stay off the social network.
  • One major element of Chris Chibnall's early drafts which was eventually dropped involved the appearance of Prime Minister Stephen Carter. Suspicious of the Doctor, Carter would bar him from the United Kingdom, resulting in the Doctor's absence from a long stretch of the narrative.
  • Brian was initially uneasy when Amy and Rory decided to take “one more trip” in the TARDIS. Steven Moffat suggested that Brian should instead encourage his son and daughter-in-law to go with the Doctor, providing a less sombre and more subtle lead-in to their departure in The Angels Take Manhattan [+]Loading...["The Angels Take Manhattan (TV story)"].
  • The episode comprised Block Three of season seven.
  • Matt Smith enjoyed working with Jemma Redgrave, describing her as "graceful, funny and charming and an absolute delight".
  • There was a deleted side-adventure where Amy and Rory defused a bomb which threatened an alien convoy. Okezie Morro and Henry Luxemburg were cast as bomb disposal experts Conroy and Sullivan.
  • This was the last episode to filmed at Upper Boat Studios. The series then transferred to Roath Lock Studios.
  • Chris Chibnal described the episode as as "a lovely big Earth invasion story" but different from the ones done before, as it focused on Amy and Rory's time with the Doctor and the impact of him on their lives. He stated it is told more from Amy and Rory's point of view than ever before, and is about celebrating them before they leave.
  • The episode originally began with scenes such as the adventure with Henry VIII and Amy at the engagement party. These were re-scheduled to introduce the invasion storyline earlier.
  • There was originally an extended action sequence where Rory took down the two orderlies who captured him.
  • The climax was originally very different. The Shakri was physically present, rather than merely appearing as a hologram. He was defeated when Amy and Rory attacked him with the syringes they had retrieved from the orderlies, and the Doctor used his sonic screwdriver on the Shakri's devastating ocular weaponry. However, it was felt that this part of the narrative detracted from the focus on Amy and Rory's life together, and so Chris Chibnall prepared new material to replace it. As a result, new material in the Ponds' house was shot.
  • Chris Chibnall was keen to revive Russell T Davies' tradition of celebrity cameos. He initially suggested the judges of either Britain's Got Talent or The Voice before settling on The Apprentice.
  • Douglas Mackinnon made a cameo as Craig, the hapless contestant on The Apprentice.
  • This was the last episode that Karen Gillan and Arthur Darvill filmed. Their last scene filmed together was getting into the TARDIS with the Doctor after saying farewell to Brian; when the doors closed they hugged Matt Smith and started crying.
  • Marcus Wilson stated that a "hundred" individual cube props were made, with "many more" added with CGI.
  • The Doctor and Amy's conversation outside the Tower of London could not be filmed at the genuine location due to the London Olympics, so it was shot on studio in Cardiff and the live action footage of them was composited with other footage of London, using visual effects to create the illusion.
  • Before being taken by android orderlies himself, Arnold Underwood was to make reference to a neighbour named Elizabeth Cracknell who had not returned home from the hospital.
  • Douglas Mackinnon had previously directed Steven Berkoff in The Flying Scotsman. He told Starburst that "The experience of working with him on Doctor Who was something that'll never be repeated; you could ask anyone on the cast or crew and they'll agree that his participation was extraordinary."
  • Kate's look of incredulous joy when the Doctor mentions her father was heavily influenced by Jemma Redgrave's own love and admiration for her late father, Corin, who had passed away only a couple of years prior to filming.
  • Steven Berkoff filmed his part in three days. Despite playing the main villain, he only has eight lines of dialogue.
  • This was Peter Cartwright's final television role. He passed away shortly afterwards.
  • Originally, the abductee who led Rory to the Shakri ship was a patient named Anne.
  • Chris Chibnall drew upon his childhood love of the Jon Pertwee era, which led to the inclusion of UNIT and Kate Stewart as a tribute to the Brigadier.


  • The episode was first broadcast in the United Kingdom on BBC One and BBC One HD on 22 September 2012. Overnight ratings showed that it was watched by an audience of 5.49 million live. The final consolidated rating rose to 7.67 million viewers, making it the thirteenth most-watched programme of the week on British television, and the fifth highest rated on BBC One.[5] The episode also received 1.3 million requests on BBC iPlayer, placing it fourth for the month on the site behind the first three episodes of the series. It also received an Appreciation Index of 87, considered "excellent".

Filming locations[[edit]]

  • Belle Vue Park, Albert Road, Penarth.
  • The satellite view depicting Rory's hospital and its environs was over the BBC's sprawling complex at White City, Hammersmith. The view is rotated 90 degrees, such that west is at the top of the screen. The building highlighted as the hospital is BBC Centre House.

Production errors[[edit]]

If you'd like to talk about narrative problems with this story — like plot holes and things that seem to contradict other stories — please go to this episode's discontinuity discussion.
  • After Kate Lethbridge-Stewart enters Amy and Rory's house, we see her take out her scanner. When she originally takes it out, her screen is facing the Doctor, and in the next shot, it is facing away from him.
  • In some shots when the cubes are counting down from 7, some cubes are missing the numbers in one shot and then have them in the next. This can be seen at 28:01 when the Doctor is in the room with the cube, and when the nurse is removing the cubes from the hospital at around 25:44.
  • When Amy lifts her legs to allow the Doctor to vacuum the floor beneath her feet, Karen Gillan's audio recorder can be seen in the back pocket of her jeans.


Home video releases[[edit]]

Series 7, part 1 DVD cover.

DVD & Blu-ray releases[[edit]]

  • The Power of Three, along with the rest of the first half of the series (episodes one through to five) was released as Series 7 Part One on DVD and Blu-ray in region 1/A on 13 November 2012, in region 2/B on 29 October 2012 and in region 4/B on 14 November 2012.
  • The short documentary A Writer's Tale focused on the making of this story.
  • Also, this episode was released as part of the Complete Seventh Series boxset on DVD and Blu-ray in region 1/A on 24 September 2013, in region 2/B on 28 October 2013 and in region 4/B on 30 October 2013.

Digital releases[[edit]]

  • In the United Kingdom, this story is available on BBC iPlayer.

External links[[edit]]


  1. 1.0 1.1 The Doctor Who Team (22 September 2012). Lord Sugar and Brian Cox: Who Knew?. BBC - Blogs - Doctor Who. Retrieved on 22 September 2012.
  3. Failes, Ian (22 May 2013). Doctor Who: Stargate’s adventures in time. fxguide. Retrieved on 20 November 2018.
  4. sfx (July 2 2012). Doctor Who Series 7: New Episode 4 Reshoot Pics. SFX. Retrieved on 23rd September 2012.
  5. Doctor Who Ratings - UK final