"Your leader will be very angry if you kill me... I'm a genius!"The TARDIS lands on 21st century Earth, and discovers that the T-Mat matter transportation system upon which the entire planet's economy now relies is broken. The Doctor and companions agree to take an elderly rocket to the Moon (which houses the relay station) and investigate.When they arrive, they discover that Ice Warriors have taken over the station and are preparing to invade Earth. They have seed pods which will be T-Matted to selected points on the Earth's surface before emitting fungus that will remove oxygen from the atmosphere, killing all humans and rendering the planet habitable for the Ice Warriors.The Doctor manages to get the T-Mat working and transports back to Earth, where he discovers that the seed pods are destroyed by contact with water (quite a big hole in the Ice Warriors' plan there). He uses the weather station on Earth to trigger a downpour, destroying all the seeds, then T-Mats back up to the moon to misdirect the approaching Martian fleet into orbiting the Sun, where they will be destroyed.Not to be confused with The Seeds of Doom
— The Doctor
- Alien Kudzu: The Ice Warriors employ pods that release a rapidly-multiplying spore, which sucks the oxygen out of Earth's atmosphere. The Doctor finds out that water counteracts the pods.
- Artistic License – Biology: The seed pods emit the fungus. Fungi grow from spores, not seeds. Though to be fair, these things are from another planet. They could be called fungi because they look like it, not because they act like it.
- Batman Grabs a Gun: The Doctor hunts and kills Ice Warriors with a heat ray.
- Break Out the Museum Piece: The rocket. Later, a motor car, though we don't get to see that.
- Corpsing: The sight of Patrick Troughton being swept off his feet by a wave of foam is too much for Wendy Padbury. She apologises profusely for it in the DVD commentary.
- Cukoloris: The launch countdown is projected onto Gia's face.
- Custom Uniform of Sexy: All the male technicians wear hideous, baggy jumpsuits. Miss Kelly gets figure-hugging Future Spandex.
- Destruction Equals Off-Switch: Averted when an Ice Warrior pulls a bunch of levers on a (very simple) control panel and then shoots it, so it'd melt and nobody could change the setting. As the system is otherwise undamaged, the Doctor is able to rewire a new setting.
- Dirty Coward: Fewsham.
- The Dog Bites Back: Even a Dirty Coward can be pushed too far.
- Doomed New Clothes: A behind-the-scenes example. Wendy Padbury liked her second costume (the leather trouser suit) so much that she bought it — and BBC bureaucracy required her to pay before the start of filming. Then, in the scene where Zoe has to crawl through a tunnel, the paint on the set turned out to be still wet.
- Dying Moment of Awesome: Fewsham, who is shot down after the Ice Warriors discover he is broadcasting their activities to an Earth station. Especially awesome because he'd been a Dirty Coward up until then.Fewsham: "Every word has been heard on Earth".
- Emotionless Girl: Gia Kelly.
- Hair Decorations: Gia seems to think she's cuter with something that looks like a coffee cup◊ attached to her hair.
- Heroic Sacrifice: Early in the story, Osgood sabotages the moonbase's equipment while pretending to help the Ice Warriors. They kill him for it, but it serves to slow them down for a good episode or two.
- Hostile Terraforming: The Ice Warriors attempt to xenoform Earth using a fungus that will extract oxygen from the atmosphere.
- Hurl It into the Sun: The humans on board the moonbase send a signal to draw the invading Ice Warriors off course into the sun.
- Kill 'em All: None of the people originally stationed at the T-Mat moonbase survive this serial. Phipps and Fewsham survive longer than the rest, but Phipps dies at the end of Part 4, and Fewsham dies in the middle of Part 5.
- The Living Dead: The spores' first victim not only breathes visibly, but his fingers twitch too.
- Man-Eating Plant: The killer Martian fungus.
- Mishmash Museum: Displays about Leonardo da Vinci, Yuri Gagarin, and Teleporters and Transporters.
- Plant Aliens
- Portal Network
- Redemption Equals Death: Fewsham
- Right Under Their Noses: An Ice Warrior misses Jamie hiding in a corner, behind nothing at all.
- Failed a Spot Check: One also completely misses Phipps while actively searching for him. All it had to do was turn around and that would've been that.
- Sequel Episode: To "The Ice Warriors".
- Stock Footage: The footage of the rocket in episode five is stock footage of Mariner 4, a mission launched in 1964 to map the surface of Mars. Notably enough, the images taken by it were sufficient to dispel belief in intelligent life on the planet.
- The footage of the rocket launch in episode six is also library footage, from a Soviet launch in 1948 of a R-1 missile, a short-range copy of the German V-2.
- Tranquil Fury: The Doctor, having spent most of the serial clowning and panicking, is frighteningly calm and restrained as he explains to the Big Bad what he has done, and why.Doctor: We sent up a satellite. That signal has sent your fleet into a false orbit.
Slaar: The heat of the sun will kill them! You have destroyed our entire fleet!
Doctor: You tried to destroy an entire world.
- Weaksauce Weakness: If your species can be wiped out or your plans crippled by something like water, setting up shop on a world with a surface that's ~70% water is ill-advised.
- Weaponized Teleportation: The Ice Warriors want to teleport the Doctor into outer space. Refusing do this is the beginning of Fewsham's Heel–Face Turn.
- The X of Y