Synopsis from: http://en.wikipedia.org/wiki/Cold_War_(Doctor_Who)
The episode opens on a Soviet submarine sailing near the North Pole in 1983, during the fear of nuclear attack known as the Cold War. A nuclear weapons launch drill they are running is interrupted by Professor Grisenko. In the submarine’s cargo hold, a sailor comes across the block of ice that Grisenko believes contains a frozen mammoth. The ice block is not due to be defrosted until the submarine docks, but the sailor begins to use a blow torch to defrost the block of ice prematurely. An arm bursts out of the ice and grabs the sailor by the throat.
The submarine begins sinking as the creature in the ice escapes and runs amok, with water pouring into the vessel. The TARDIS materialises inside the submarine; Clara and the Doctor tumble out, believing that they are in Las Vegas. Although the sailors try to restrain them, the Doctor convinces Captain Zhukov to maneuver the submarine off to the side, landing it safely and preventing it from imploding. During this the TARDIS inexplicably dematerialises. The Doctor tells the captain and his crew that he and Clara are time travelers. They then encounter the Ice Warrior, Grand Marshall Skaldak. The Doctor convinces them that they must be peaceful, but a frightened soldier shocks Skaldak from behind with a cattle prod knocking him out cold. The chained Skaldak calls for his brothers to find him.
The Doctor convinces Captain Zhukov that someone must speak to Skaldak. The Captain insists but the Doctor refuses, saying that as an enemy soldier, Skaldak will not talk to him. Zhukov refuses to let the Doctor do it. As the only one who knows the Ice Warriors, the Doctor is too valuable to risk. Clara volunteers, and although reluctant, the Doctor allows her to go. Wearing headphones and lip mic she begins to relay the Doctor’s words to Skaldak, but he knows that the Doctor is listening. After learning that he has been encased in the ice for 5000 years Skaldak laments the loss of his daughter and his people. Skaldak escapes from his armor, and stops broadcasting the signal to the other Ice Warriors, believing himself to be the only one of his kind left. The Doctor surmises that, thinking himself alone in the universe, Skaldak has nothing left to lose.
Hiding in the dark corners of the submarine, Skaldak manages to grab and kill three members of the sub’s crew before the Doctor and Clara catch up to him. Finding the crewmen’s remains, the Doctor surmises that the killing was “forensic” and that Skaldak is seeking to analyze the humans’ strengths and weaknesses. After learning of the ongoing Cold War and the mutually assured destruction, Skaldak informs them that he plans to use the submarine’s nuclear missiles to provoke a global thermonuclear war and destroy humanity as revenge for the humans attacking him earlier, as under Martian code humanity as a whole has declared war on the Ice Warrior race. Reaching the bridge, he is able to connect himself to the sub’s missile guidance systems and activate the double-keyed arming sequence. The Doctor attempts to persuade Skaldak to show mercy, and has almost succeeded when the sub is rocked by the impact of a tractor beam from above. The Ice Warrior’s people have arrived in a spaceship hovering over the site of the sub’s undersea grounding, and haul it to the surface with their beam through the packed polar ice.
Skaldak is beamed aboard the Ice Warriors spaceship, though the missile launch system is still active. Showing mercy, Skaldak deactives the missiles remotely. When the Doctor’s sonic screwdriver informs him the TARDIS has reappeared, he informs Clara that it had “relocated” automatically as part of the H.A.D.S. (short for “Hostile Action Displacement System”) which the Doctor had reactivated shortly before. However, the TARDIS reappeared at the South Pole, and so the Doctor is forced to sheepishly ask Zhukov for a lift.
Discuss.