The Doctor, Ian and Susan discover that they have exposed to radiation.
The Daleks have conquered the Earth. Susan and Barbara have joined the human resistance who launch an attack on the Dalek flying saucer where the Doctor and Ian are prisoners.
Barbara realises how to control the Robomen and orders an attack on the Daleks.
The Daleks follow the TARDIS to the jungle world of Mechanus, infested with lethal plants. There, the Daleks release a robot double of the Doctor that is programmed to kill.
