The Doctor, Jamie and Victoria arrive on Telos, where an archaeological group are exploring the Tomb of the Cybermen. But are the Cybermen as dormant as they believe?
The Yeti escapes from the monastery and Victoria and Thonmi are accused of assisting it, while the Doctor and Jamie endure a perilous journey back across the mountains.
The Doctor persuades Bruce to help him infiltrate Salamander's research centre while Salamander takes drastic action to prevent Swann finding out the truth.
The Doctor and Victoria are taken back to the Goodge Street base by Colonel Lethbridge-Stewart where the Doctor becomes convinced there is a traitor in their midst.
With Travers having been captured by the Yeti, the Doctor attempts to find a way to gain control of the robots while Lethbridge-Stewart tries to recover the TARDIS.
The Doctor, Jamie and Victoria are taken prisoner by the staff of a gas refinery, who have lost contact with their drilling rigs and experienced mysterious drops in pressure.
With the Weed Creature poised to burst out of the pipeline and attack the base, an encounter with Oak and Quill gives the Doctor a vital clue about its weakness.
The Doctor and Jamie are brought aboard the Wheel where Jamie is horrified to learn the crew plan to destroy the Silver Carrier with the TARDIS on board.
The Cybermen gain control of more members of the Wheel crew and the Doctor realises the only way to stop them is for Jamie and Zoe to make a dangerous space walk.
