Patrick Troughton
The Seeds Of Death

The TARDIS materialises on Earth in the 21st century inside a private space museum. A monitor shows that all travel on the planet is now done using the T-mat system providing instant trans-mat from point to point, including the moon.

The base on the moon appears to be non-functional, but the truth is that it has been invaded by the Ice Warriors. The Doctor, along with Jamie and Zoe, assist a London T-mat station by travelling up to the moon in an antiquated rocket - they are the only people with the necessary experience.

The Doctor finds that the Ice Warriors have taken over the moon base. Using the T-mat system they transport seed pods to Earth. The pods produce a strange foam that is able to suck the oxygen out of the Earth atmosphere.

The only way to disperse the pods is by water. An Ice Warrior transports to a weather station and locks the controls so that rain is not produced. The Doctor is able to rewire the controls and produce rain, dispersing the foam. Using a satellite he is able to draw the Ice Warrior fleet into orbit around the sun. The heat destroys them.