The TARDIS narrowly avoids becoming engulfed in a cobwebby substance in space. It arrives in the London Underground railway system, the tunnels of which are being overrun by the web and by the Great Intelligence's robot Yeti. The time travellers learn this crisis was precipitated when Professor Travers, whom they first met in the Himalayas some thirty years earlier, accidentally caused one of the Yeti to be reactivated, opening the way for the Intelligence to invade again.
Social & External

The Doctor

Jamie McCrimmon

Victoria Waterfield

Colonel Lethbridge-Stewart

Professor Travers

Anne Travers
Harold Chorley
Captain Knight
Staff Sgt. Arnold
Corporal Blake
Corporal Lane
Craftsman Weams
Driver Evans
Soldier
Soldier
Yeti

Yeti
Yeti
Yeti
Yeti

Yeti