He's got a printed circuit where his heart should be.
— Penley doesn't think much of his colleague Clent.
Earth is in the grip of a new Ice Age, and the Doctor arrives at a station tasked with keeping the ice at bay using an ioniser. As the glacier moves forwards, a frozen creature is dug out of the ice - a reptilian-looking humanoid jokingly termed an "Ice Warrior" by the base personnel.
The Ice Warrior thaws and wakes up, stating his name is Varga and it was the commander of a ship from "the Red Planet" which crashed on Earth thousands of years ago. Now that his own planet is dead, Varga plans to conquer earth with the help of his similarly-frozen comrades.
The base scientists meanwhile realize that if the ionizer beam hits the alien ship, the engines could explode and kill them all - but the Doctor persuades them it's worth the risk as not doing so could doom the entire Earth. Luckily for all concerned (except the Ice Warriors), there's only a relatively small explosion - killing all the Ice Warriors and destroying the ship and also conveniently stopping the flow of the glaciers for a while.
The Ice Warriors would recur several more times and had been planned for a story with the Sixth Doctor before cancellation put paid to that. And the Seventh, before it was cancelled again. They most recently reappeared in the Eleventh Doctor episode "Cold War
- An Iced Reptile: The Ice Warriors.
- Arm Cannon: How the sonic blasters are carried.
- Artistic License - Biology: The stated reason for the Earth's new Ice Age is the reduction of plants reduced the amount of Carbon Dioxide in the air, causing global cooling. Plants consume Carbon Dioxide and turn it into oxygen.
- Change the Uncomfortable Subject:
Jamie: You see how those lassies were dressed?
Victoria: Well, I think it's disgusting, wearing that kind of thing.
Jamie: [Mocking] Oh, aye, so it is, so it is. You er, you don't see yourself dressed like that then?
Jamie: Oh, I'm sorry, it was just an idea.
Victoria: We will now change the subject, please.
- Explosive Decompression: The cliffhanger to Episode Four, according to the Doctor. Tsk tsk.
- Face-Heel Turn: Penley's friend Storr tries this. The Ice Warriors aren't interested.
- Hey, It's That Guy!: Wallace is Elric Penley.
- Hidden Depths: At the end of the episode, Clent surprises Penley by telling him that he never uses a computer to write his reports for him.
- Logic Bomb: A minor one happens when the science team asks the computer a question where any answer carries the risk of the computer being destroyed. Being programmed for self-preservation, the computer more or less crashes, but there's no actual physical damage to it.
- Make Me Wanna Shout: The Ice Warriors specialize in sonic weaponry.
- Master Computer: A milder version than most. The computer doesn't run anything itself, but everyone relies on it to give instructions based on the data they input.
- Missing Episode: This story is largely intact, with only episodes two and three (of six) missing. Until the return of "The Enemy of the World" and "The Web of Fear", it was the only story from Troughton's first two seasons that was anywhere near being complete, with the exception of "The Tomb of the Cybermen". In August 2013, the serial was released on DVD for the first time, with the missing episodes restored using animation.
- Namedar: In subsequent stories the Martians are actually called the Ice Warriors.
- Panty Shot: A member of the female base crew's short uniform (Jamie wants to see Victoria in one, which more or less happens with Zoe [with a ladder-climbing scene] in The Invasion) doesn't quite cover for having to get up after a sonic blast that hits the base.
- Snake Talk: The Martians speak in whispered, sibilant tones.
- Verbal Tic: Sorta. The hissing.