Trying to defect, Major Ivan Kuchenko is trapped inside a hotel room with Commissar Vassiloff, a hitman, and Boris, his assistant, in the room across the street. Vassiloff has planted a bomb in the room and Ivan must find it within three hours or be blown to bits.

The alien world of Marinus. Perfect peace has reigned here for decades due to the mind-controlling influence of a machine known as the Conscience. But now a race known as the Voord have developed an immunity and Arbitan, keeper of the machine, has been forced to scatter the vital control keys around the planet. Now he needs the help of the time travellers to get them back - it will be an extraordinary journey, with perils every step of the way...