The Keys of Marinus: On a remote island of glass surrounded by a sea of acid, there is a machine that can remove evil from the minds of an entire population - the Conscience of Marinus. Fearful of it's immense power falling into the wrong hands, it's sole guardian has scattered the machine's operating keys across the planet. The TARDIS crew arrives to find the island under attack by the evil Voord. Marinus' last line of defense - and it's only hope - is the Conscience machine. The Doctor and his companions must undertake a deadly quest to recover the keys of Marinus. The Twin Dilemma: The Doctor has regenerated and all is not well. Confused, angry and acting strangely, the new Doctor decides to become a hermit, so takes his concerned companion Peri to a desolate asteroid where he plans to live for several centuries. The time travelers soon uncover a plot that threatens the entire galaxy. But why has an alien gastropod kidnapped twin boys from Earth, and will the Doctor recover in time to find out?