Ace's timeline

By several accounts, the Seventh Doctor's companion Ace had a unique timeline which was heavily interfered with on multiple occasions, (PROSE: Interference, At Childhood's End, Sometime Never..., AUDIO: Assassins) leading to it being fractured across multiple possible timelines. (PROSE: At Childhood's End, AUDIO: Signs and Wonders)

Known meddling

Fenric was the initial augmenter of Ace's timeline, positioning her into a Wolf of Fenric. In a process similar to but more intentional than the Eighth Doctor's alterations to Sam Jones's timeline, the Seventh Doctor undid Fenric's manipulations using temporal equations. As these equations were done instinctively, Ace's new destiny didn't go quite as the Doctor expected. (PROSE: Interference)

Ace and the Doctor visited the last resting place of the Wraiths, interdimensional beings that existed in multiple timelines simultaneously, and the home of the Astingir, where unbeknown to her, the Doctor planned to check on the Quantum Anvil - a temporal possibility engine created by the Astingir in their war with the Wraiths which shattered the time streams of the latter into infinite potential outcomes leaving them intangible. He hoped Ace would make contact with the Anvil, enabling her to act as an emissary with the Wraiths. After being grabbed by the Wraiths when she stood too close to their containment, Ace made contact with the Anvil which imbued her with the ability to commune with the Wraiths. She also saw her life splinter into different outcomes, seeing multiple different possible timelines of her future. (PROSE: At Childhood's End)

During their attempt to create their own reality, the Council of Eight sought to weaken the Doctor's timeline by killing his companions prematurely. (PROSE: Sometime Never...) The Seventh Doctor learned of Ace's death in advance. (PROSE: Prime Time) Shortly after Ace was murdered by George Limb in 1959, temporal disruptions from Limb's flawed time machine created a version of Ace from a slightly divergent timeline as various realities collapsed together. This Ace continued travelling with the Doctor. (PROSE: Loving the Alien) Many of the Council's alterations were undone following their defeat by the Eighth Doctor. (PROSE: Sometime Never...)

After abandoning her on Earth during the Last Great Time War, (AUDIO: Soldier Obscura) Irving Braxiatel meddled in Ace's timeline as early as her travels with the Doctor. This meant Narvin was unable to track either of them down. (AUDIO: Assassins) Braxiatel also altered Ace's memories. (AUDIO: Soldier Obscura)

Outcomes

Ace's contact with a Quantum Anvil showed her multiple future outcomes of her travels with the Doctor. These included:

• Living on Gallifrey, (PROSE: At Childhood's End) where she trained at the Time Lord Academy and worked for the Celestial Intervention Agency, serving during the beginning of the Last Great Time War. (AUDIO: The Lights of Skaro, Dominion, Intervention Earth, Enemy Lines, Soldier Obscura)
• Travelling in the TARDIS with a dark haired woman. (PROSE: At Childhood's End)
• Fighting Daleks, (PROSE: At Childhood's End) whilst serving with Spacefleet for three years in the 26th century. (PROSE: Deceit)
• Living with an ancestor of Sorin, (PROSE: At Childhood's End) Nikolai Sorin. (PROSE: The Curse of Fenric, Set Piece)
• Dying in a Nitro-9 explosion, (PROSE: At Childhood's End) which she caused to destroy the Lobri. (COMIC: Ground Zero)
• Growing old in the Doctor's company. (PROSE: At Childhood's End)

According to Ace's memories, shortly after her exposure to the Quantum Anvil Ace declared she was leaving the Doctor. After returning to Earth, she founded A Charitable Earth and years later encountered the Thirteenth Doctor. (PROSE: At Childhood's End)

By another account, Ace first encountered the Thirteenth Doctor, along with Yasmin Khan and Graham O'Brien, when she was embroiled in the Master's Dalek Plan in 2022; by that point, she had not seen the Doctor in three decades. The Spy Master suggested that Ace had been "ditch[ed]" by the Doctor after a "fall out". Indeed, Ace acknowledged that she had "fell out" with the Seventh Doctor, for which she apologised when given the opportunity to speak to an AI hologram of him, to which he assured her that they were not only "good" but "ace". (TV: The Power of the Doctor)