When something disturbs the TARDIS in flight, the Sixth Doctor is determined to find out the reason why. Landing in London, 1985, he and Peri are shocked to find the Cybermen are hiding in London"s sewers! Becoming their prisoner, the Doctor is forced to take the Cybermen to their home planet, Telos. There he discovers the inhuman monsters have captured another time vessel and plan to change history. They want to redirect Halley"s Comet so it crashes into Earth in 1985 ? the year before their original home planet, Mondas, was destroyed.PERIPerpugilliam Brown, known as Peri, was an eighteen year?old American Botany student holidaying in Lanzarote with her step?father, when the Fifth Doctor and Turlough landed nearby. Turlough rescued Peri when she tried to swim to shore from her uncle"s boat, and took her inside the TARDIS to recover.The TARDIS took off with Peri still on board. Headstrong and argumentative, Peri stayed with the Doctor and helped him through his most difficult regeneration to date. Peri"s fate is unclear.