The Sixth Doctor (Colin Baker) wants to fix the chameleon circuit, show Peri Haley’s Comet, answer a distress signal, and shut Peri up, so he lands in London in 1985. However, the Cybermen have beat him there, having come from the far future and want to avert the destruction of Mondas. Lytton (from some other story) returns to rob a bank…no not really, but don’t tell his henchmen. Also, the Doctor decides an ass-whooping is called for, and it’s him versus everyone.
Steve also decides to fix the TARDIS’s chameleon circuit, but Andrew isn’t impressed. The TARDIS is really out of practice.