The Doctor and Dodo return to London in the present day where the Doctor becomes concerned about WOTAN, a new super-computer installed in the Post Officer Tower.

Dodo is under the control of WOTAN and attempts to lure the Doctor into a trap, while the rest of WOTAN's slaves begin construction on its robotic War Machines.

Ben tries to escape from the warehouse but is captured by Polly, who is now also under WOTAN's control, and forced to work on construction the War Machine.

The first War Machine is defeated but the Doctor only has a matter of hours to destroy WOTAN before the rest of its army is activated.

21st century Earth is entirely dependent on the T-Mat transport system but the control centre on the moon has stopped functioning. Meanwhile, the Doctor, Jamie and Zoe meet the one man who can solve the crisis.

Eldred agrees to supply a rocket for travel to the moon and the Doctor, Jamie and Zoe volunteer to crew it.

The Doctor, Jamie and Zoe make it to the moon and join forces with Phipps but the Ice Warriors have gained control of T-mat.

The Ice Warriors' seed pods beginning materialising all over the globe while Slaar decides to kill the Doctor by T-matting him into space.

The Doctor and his allies manage to return to Earth via T-mat only to find the Ice Warrior has attacked the weather control station.

The Doctor manages to create a rain storm to destroy the Martian fungus before trying to find a way to stop the Ice Warriors' invasion fleet.

While the Brigadier investigates a loss of contact with Mars Probe 7, the Doctor realises signals coming from the probe are of extra-terrestrial origin.

UNIT retrieve the returned Recovery 7 but then Carrington hijacks it while the Doctor and Liz try to decode the signal he sent.

Carrington is holding the astronauts at a secret location but when he takes the Doctor, Liz and the Brigadier there they find they have been kidnapped.

Liz has been captured by Reegan's men and the Doctor begins to suspect Taltalian is more involved than he appeared.

The Doctor decides to take Recovery 7 back into space to search for the missing astronauts but Reegan sabotages the launch.

The Doctor speaks with the alien captain and learns the astronauts sent to Earth were ambassadors. However, before he can alert the authorities he is kidnapped by Reegan.

Carrington is planning to expose the aliens on live television and call for an interplanetary war and the Brigadier must rescue the Doctor and Liz in time to stop him.

When a mysterious object lands near the Nuton power complex, UNIT investigate and encounter the Axons, a group of aliens who offer the mineral axonite, which can duplicate matter, as a gift.

The Doctor and Winser begin to analyse axonite while Chinn plots to secure its use exclusively for Britain.

The Doctor and Jo are being held prisoner by Axos while Chinn is forced to organise the worldwide distribution of axonite and the Master returns to the power complex to try and steal the TARDIS.

The Doctor and Jo escape from Axos but then the Doctor offers the Master a deal; if he helps him repair the TARDIS, they can flee Earth together.