Harry Towb

Earth, the near future. The Master - another renegade Time Lord and the Doctor's sworn enemy - arrives and allies himself with the Nestene Consciousness in an attempt to conquer the planet.

Attempting to find out where Jo encountered the Master, the Doctor heads to the circus where he falls foul of Rossini.

Ice Warriors on the moon plan to make the Earth's atmosphere inhospitable to humans; teleportation technology T Mat transports people and objects around the globe; the Doctor visits a rocket museum.