An English submarine dives into cold black water. Sailors scamper to and fro as an English voice says, "The signal is genuine!" This is the Captain's cue. He gives the order to launch nuclear weapons, also in English. "Moscow confirms launch sequence!" someone says, because the sub is actually Russian and so is her crew. The TARDIS is so powerful that it translates for us several minutes before it even arrives! The Captain reaches out to push the button that will plunge the globe into nuclear war. Suddenly, David Warner strolls onto the bridge, singing "Vienna" by Ultravox. Everyone's like, "What's David Warner doing on the bridge singing 'Vienna' by Ultravox?" He notices them staring at him and asks, "Did I interrupt something?" The Captain explains, "We were about to blow up the world, Professor." The Captain calls off the drill. His first officer (I guess) flounces off because he wants to keep running drills. "Did you have your specimen stowed okay?" the Captain asks. "Yes, Piotr's looking after it," says the Professor, except he pronounces it "Peter" despite how the CC spells it.
They talk about how the specimen is probably a mammoth, even though as the camera pans down to the hold, it's clear that the shape within the block of ice is about as elephantine as the crew are Russian. Piotr doesn't want to wait until they get to Moscow and decides to take a torch to the ice. There is no reason for this to happen except that the story needed it to happen. I'm surprised that Mark Gatiss wrote this episode, considering I generally find his work much more skillful. Anyway, Piotr thaws the ice just enough that an armored fist is able to punch through from within and grab him by the throat. Good things come to those who wait. Death and destruction come to those who don't.
By the time the opening credits are over, the sub is in quite a state of panic. The creature freed from the ice has been causing so much havoc that the ship is now sinking fast and taking on water. The TARDIS whomp-whomp-whomps onto the bridge and out pops the Doctor in Elvis sunglasses. "Viva Las Vegas!" he shouts an instant before he and Clara tumble out. They should have made a left turn at Albuquerque. The Captain is quite aghast at their sudden arrival, but has more pressing matters at hand. The Doctor quickly assesses the situation, babbles something about turbines and momentum, and suggests the Captain maneuver the sub laterally. His sonic screwdriver has picked up an underwater ridge nearby. They can land on it! Or break apart on it! The sub groans under the increasing pressure. The Captain gives the order to follow the intruder's suggestion, much to his first officer's dismay.