Ice Warrior Awakens
A Soviet submarine is sailing near the North Pole in 1983 during the Cold War. The TARDIS inexplicably dematerialises, leaving The Doctor and Clara to face the escaped Ice Warrior, Grand Marshall Skaldak.
Mutually Assured Destruction
Having learnt of the ongoing Cold War and the doctrine of mutually assured destruction, Skaldak plans to use the submarine's nuclear missiles to provoke a global thermonuclear war and destroy humanity. Who will blink first!?!