Key to Time

The Key to Time is a powerful and mythic artifact with which the Guardians of Time used to maintain control over universal order and chaos. Its shape was that of a perfect, crystalline cube.

The Key to Time was originally created to wiped the memories of the participants of the Millennium War, though it later gained a more general purpose. (DW: The Quantum Archangel)

Millennia later, when universal balance was upset, the White Guardian enlisted the Doctor and Romana to gather the Key's six segments. (DW: The Ribos Operation) The Black Guardian used the Shadow to stop the Doctor from obtaining the sixth segment. After the Doctor defeated the Shadow, he assembled the Key and outwitted the Black Guardian, enabling the White Guardian to restore universal balance. The Key was then broken apart and scattered throughout the universe again, assuming five new shapes and restoring Princess Astra to her natural form. (DW: The Armageddon Factor)

They found the segments disguised as:

• A lump of Jethrik crystal taken to Ribos by Garron (DW: The Ribos Operation)
• The pillaged planet Calufrax, now shrunk down to football size by the Zanak. (DW: The Pirate Planet)
• The former Great Seal of Diplos, kept in the form of a necklace on Earth by Cessair. (DW: The Stones of Blood)
• A Taran statue. (DW: The Androids of Tara)
• A holy relic of the Swampies, swallowed by Kroll on a Delta Magna moon. (DW: The Power of Kroll)
• Princess Astra of Atrios. (DW: The Armageddon Factor)

Years later, the White Guardian sent the Doctor, Ace and Benny on a quest to find the six segments of the Key to Time, scattered across the Doctor's personal past, and disguised as items connected with him in some way. (DWM: Time & Time Again)

• The Doctor's hat, which Benny obtained from him in the Land of Fiction.
• A jelly baby with a missing leg, which Benny took from the Doctor while chased by Mandrels on the stolen section of the planet Eden.
• A fencing sword used by the Doctor to parry with Ace in Sir Reginald Styles' mansion.
• A cricket ball hit by the the Doctor at Lord Cranleigh's party.
• A cat badge formerly owned by the Doctor's sixth incarnation, reluctantly given to his next incarnation.
• The TARDIS instruction manual dropped by the first incarnation of the Doctor as his own seventh incarnation saved his life.

Other information

At some stage, the Master obtained a segment of the Key to Time and used it to tear apart the constellation of Mandusus. (MA: Cold Fusion)