At the close of the 21st Century, T-Mat teleportation has replaced every other form of travel. Even space-travel has ceased. The TARDIS crew arrive in an Earth museum dedicated to obsolete rocket technology, run by Professor Daniel Eldred (Philip Ray). The T-Mat station on the Moon has broken down. Commander Radnor (Ronald Leigh-Hunt) and Gia Kelly (Louise Paso) call the Professor for help. He has been building a rocket, hoping to re-ignite interest in space-travel. The Doctor, Jamie, and Zoe volunteer to be the crew.

The Lunar station has been over-run by Ice Warriors from Mars, who want to invade Earth. When they arrive, the earth-rocket crew contact Phipps (Christopher Coll) who is hiding there. The Doctor is discovered by the Ice Warriors and their commander Slaar (Alan Bennion). The invaders intend to send seeds of a fungus to Earth by T-Mat, where it will spread and suck up all the oxygen, leaving the planet like Mars. They begin at once and send a small contingent to Weather Control to make sure conditions are perfect for the spread of the virus.

The Doctor and his forces capture Weather Control and bring about a driving rain, which kills the Martian fungus. The Doctor returns to the station on the moon and sends a false signal to the incoming Ice Warrior fleet, sending it into the Sun.

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Part 6