Patrick Troughton
The Web Of Fear

The TARDIS is attacked in space by a mysterious web-like substance, and is forced to land, whereby it materialises at a London Underground station. The rail tunnels have also been overrun by the web substance, and also by robotic Yeti.

Professor Travers, whom the Doctor and Victoria first met in the Himalayas, has accidentally caused one of the Yeti to become activated, paving the way for another invasion attempt by the Great Intelligence.

The Doctor works with the military, led initially by Captain Knight, and later Colonel Lethbridge-Stewart. However, Staff Sergeant Arnold's mind has come under the control of the Great Intelligence, and this hampers Lethbridge-Stewart's investigations.

The Great Intelligence has created a device that will allow it to steal the mind of the Doctor. The Doctor manages to reverse the polarity and can use the device to feed off the Great Intelligence. He almost succeeds, until he is rescued, and the Great Intelligence is repelled into space.