Written by Brian Hayles and an uncredited Terrance Dicks and directed by Michael Ferguson, it originally aired in six weekly parts on BBC1 from 25 January to 1 March 1969.
In the serial, the time traveller the Second Doctor (Patrick Troughton) and his travelling companions Jamie McCrimmon (Frazer Hines) and Zoe Heriot (Wendy Padbury), along with the technicians Gia Kelly (Louise Pajo) and Phipps (Christopher Coll), try to prevent the Ice Warriors' plot to make the Earth's atmosphere inhospitable to humans but viable for the Ice Warriors to invade.
At the end of the twenty-first century, a teleportation technology called "T-Mat" has replaced all traditional forms of transport, allowing people and objects to travel instantly anywhere on Earth.
The Doctor, Jamie McCrimmon and Zoe Heriot arrive in a museum on Earth run by Professor Daniel Eldred dedicated to the obsolete technology of rockets.
With communications out, and no way to reach the Moon without T-Mat, those responsible for the system, Commander Radnor and his assistant Gia Kelly, turn to Professor Eldred to help.
The relay station on the Moon has been invaded by Ice Warriors, a militant Martian race, who plan to use it as a staging point for an invasion of Earth.
The Ice Warriors have a deadly plan: they have seeds, which they send to various parts of Earth using T-mat, of a fungus that will multiply and suck all the oxygen from the surrounding atmosphere, making it more comfortable for the Martians but uninhabitable for humans.
Once the full T-Mat relay is repaired, one seed is sent to Earth Control and explodes, killing a technician and alerting Radnor and Eldred of the danger.
The Ice Warriors also use T-Mat to dispatch a small advance force to seize Earth's weather control systems in London and ensure good conditions for the growth of the fungus.
This explains where the Ice Warrior beamed to Earth has gone, and the Doctor tracks him down to the weather control system, where the alien has been stationed to prevent any rain fall that would be deadly to the pods.
The Doctor and his allies recapture the weather control system and summon rain, destroying the fungus, which is used to the dry conditions on Mars.