The Paradox Planet (audio story)

 was the third story in the fifth series of the Fourth Doctor Adventures, produced by Big Finish Productions. It was written by Jonathan Morris and featured Tom Baker as the Fourth Doctor, Lalla Ward as Romana II and John Leeson as K9.

Publisher's summary
Whilst travelling in the vortex, the TARDIS is struck by an advanced war machine — a Time Tank! Losing Romana, the Doctor and K9 pursue the Tank to Aoris, a world quite literally at war with itself.

Soldiers from the future are attacking the past of their own planet — gathering resources and stealing endangered species. But the past is not without weapons of its own — leaving deadly devices ready to trigger many years ahead after their enemies have been born.

Trapped at opposite ends of a temporal war, the Time Lords have two time zones to save. But who is in the right, and who in the wrong? And when history itself is against you, can anybody actually win?

Part one
to be added

Part two
to be added

Cast

 * The Doctor - Tom Baker
 * Romana - Lalla Ward
 * K9/Machina - John Leeson
 * Drang - Simon Rouse
 * Embery - Tom Chadbon
 * Fyrax - Paul Panting
 * Shola - Emma Campbell-Jones
 * Tyrus - Laura Rees
 * Lostar - Bryan Pilkington
 * Medea - Jane Slavin
 * Valchak - John Banks

Continuity

 * The Doctor tries to play the violin but does so badly. During his eighth incarnation, he would become a virtuoso on the planet Hitchemus. (PROSE: The Year of Intelligent Tigers)
 * A vessel once again tries to materialise in the same space as the TARDIS. (TV: The Pirate Planet)
 * Romana still has her sonic screwdriver. (TV: The Horns of Nimon; AUDIO: Wave of Destruction, The Labyrinth of Buda Castle)