Siberia at the end of the 19th Century, and the TARDIS arrives just as a shooting star hurtles to the ground.
With it comes an illness that affects the Doctor and Susan, and knowledge that must not fall into the wrong hands.
With his friends either dying or lost, Ian Chesterton must save the future and win the ultimate prize – a way home to 1963…
Written By: Richard Dinnick
Directed By: Lisa Bowerman
William Russell (Ian Chesterton), Tim Chipping (Grigory)
Producer David Richardson
Script Editor Jacqueline Rayner
Executive Producers Jason Haigh-Ellery and Nicholas Briggs