The Four Doctors (audio story)

The Four Doctors was Big Finish's subscribers' free release for 2010.

Publisher's summary
The fifth incarnation of the Doctor has been allowed access to the Vault of Stellar Curios, where the biomechanoid Jariden are at least prepared to consider his warnings about dangerous temporal leakage. Suddenly, out of nowhere, the Daleks attack, unleashing a temporal maelstrom that will not only threaten the Jariden race, but will have dire consequences for the history of the Doctor himself.

Plot
The Fifth Doctor investigates the Vault of Stellar Curios, where he has observed evidence of time leakage. But then the Daleks attack, looking for the contents of the mysterious vault. The Eighth Doctor also shows up and he and his former self create a time loop trap, spanning between their lives. This sends the Daleks to the Seventh Doctor's encounter with Michael Faraday in 1854 and the Sixth Doctor's visit to an early Dalek battlefield.

Cast

 * The Doctor - Peter Davison
 * The Doctor - Colin Baker
 * The Doctor - Sylvester McCoy
 * The Doctor - Paul McGann
 * Professor Kalinda / Lady Cowen - Ellie Burrow
 * Colonel Ulrik / Whitmore - David Bamber
 * Professor Michael Faraday / Magran - Nigel Lambert
 * Roboman / Jariden device - Alex Mallinson
 * Voice of the Daleks - Nicholas Briggs

Continuity

 * The Dalek Prime is in command of the Dalek assault vessel which boards the Vault of Stellar Curios (PROSE: War of the Daleks) while a Special Weapons Dalek is among the Dalek forces (TV: Remembrance of the Daleks). Both are sent back in time to the home of Professor Michael Faraday in London in 1854.
 * The Daleks used Robomen during the Battle of Pejorica. (TV: The Dalek Invasion of Earth)
 * The Fifth, Sixth and Seventh Doctors all previously met each other in AUDIO: The Sirens of Time. The Fifth and Sixth Doctors also met each other in AUDIO: Peri and the Piscon Paradox. On that occasion, the Sixth Doctor disguised himself as a Piscon named Zarl so his younger self did not realise his identity. The Fifth and Seventh Doctors also met on at least two other occasions, namely in PROSE: Cold Fusion and prior to the events of AUDIO: The Veiled Leopard. Furthermore, the Eighth Doctor previously met his three immediate predecessors (as well as his first four incarnations) in PROSE: The Eight Doctors. Given that the Seventh Doctor failed to recognise his immediate successor on this occasion, it is logical to assume that none of the first seven Doctors retained any memory of meeting their future self.
 * The Eighth Doctor remembers speaking to the Fifth Doctor over the intercom from the perspective of his younger self as well as other details of his fifth incarnation's visit to the Vault of Stellar Curios such as meeting Kalinda. This is similar to AUDIO: Peri and the Piscon Paradox, PROSE: Cold Fusion and TV: Time Crash in which the Sixth, Seventh and Tenth Doctors respectively remember the events portrayed from the point of view of their fifth incarnation.
 * The Seventh Doctor previously visited 1854 when he and his companions Ace and Hex travelled to Scutari and Sebastopol in September of that year during the Crimean War (1853-1856). (AUDIO: The Angel of Scutari)
 * The Seventh Doctor fails to recognise his immediate successor. However, during his sixth incarnation, he along with his companion Evelyn Smythe observed two Eighth Doctors, Charley Pollard, C'rizz and Lucie Miller meeting in an American frontier town in the 1870s. (AUDIO: The 100 Days of the Doctor)
 * The Daleks use rels as a unit of measure of time. (COMIC: The Emissaries of Jevo onwards)