Astronauts rescued from a mission to mars are kidnapped when they arrive back on earth. They seem to have been irradiated, and can now kill people merely by touching them. But the Doctor discovers the astronauts have been replaced with Alien ambassadors who are being forced to behave in a hostile manner. With The Doctor traveling to the alien mother ship, and Liz kidnapped, The Brigadier is left wondering who to trust.

Aided by his two assistants Jamie and Victoria, the Doctor lands the TARDIS on Telos, last resting place of the infamous Cybermen. There he discovers a band of archaelogists on a secret expedition to unearth the reason for his old enemies' extinction. In the underground shadowy depths, they find the icy tomb. A whole army in hibernation. A threat to no one, if the temperature remains low. But if the traitor in their midst gets his way, things could really heat up.

A former British spy stumbles into in a plot to overthrow Communism with the help of a supercomputer. But who is working for whom?

The TARDIS lands in a space museum on Earth in the late 21st century, where the Second Doctor, Jamie and Zoe learn that contact has been lost between Earth and the Moon. In this era, instant travel — T-Mat — has revolutionised the Earth. Its people have lost interest in space travel. The Doctor and his companions travel to the Moon in an old-style rocket and reach the Moonbase, control centre for T-Mat, only to find a squad of Ice Warriors have commandeered the base and plan to use the T-Mat network to their advantage.

Mysterious forces are at work in 1930s Tibet. The once gentle Yeti have turned savage and besieged a Buddhist monastery. The Second Doctor, Jamie and Victoria arrive expecting a friendly welcome from the abbot, but soon become ensnared in the plans of the extradimensional being known as the Great Intelligence.

The TARDIS arrives on Earth in a new ice age. The travellers make their way into a base where scientists, commanded by Leader Clent, are using an ioniser device to combat the advance of a glacier.

Inspector Maigret responds to a call from a young woman in the middle of the night, but he then finds himself accused of raping her. He is forced to clear his name, and search for what had really taken place that night.