An American private-eye arrives in Alphaville, a futuristic city on another planet which is ruled by an evil scientist named Von Braun, who has outlawed love and self-expression.
A woman wakes up on a distant planet and finds the crew of her space station viciously killed. Her investigation into what happened sets in motion a terrifying chain of events.
The TARDIS arrives on the planet Marinus on an island of glass surrounded by a sea of acid. The travellers are forced by the elderly Arbitan to retrieve four of the five operating keys to a machine called the Conscience of Marinus, of which he is the keeper. These have been hidden in different locations around the planet to prevent them falling into the hands of the evil Yartek and his Voord warriors, who plan to seize the machine and use its originally benevolent mind-influencing power for their own sinister purposes.
On the planet Vortis, the Doctor and his companions aid the butterfly-like Menoptra in their battle against the parasitic Animus and its mind-controlled minions, the ant-like Zarbi.
A colony trying to regain the suddenly terminated lines of connection to the earth that now threatens their existence.