In a Mars base, the inhabitants are being infected by a mysterious water creature which takes over its victims. The Doctor is thrust into the middle of this catastrophe, knowing a larger one is waiting around the corner.
David Tennant
The Doctor
Lindsay Duncan
Captain Adelaide Brooke
Peter O'Brien
Ed Gold
Sharon Duncan-Brewster
Maggie Cain
Gemma Chan
Mia Bennett
Aleksandar Mikic
Yuri Kerenski
Michael Goldsmith
Roman Groom
Cosima Shaw
Steffi Ehrlich
