In the 23rd century, people live in a great domed city and a utopian society, except for one catch: no one lives past age 30. Every citizen has a crystal in their palm, which counts down your "lifeclock." When they reach 30, a person must undergo a ritual which may reknew, or leave them dead. Logan 5 (Michael York) is a Sandman, a government agent who tracks down Runners, people fleeing the ritual and trying to escape to the outside world. Sandmen kill Runners and, like Logan's partner Francis (Richard Jordan), expect to be renewed when their clock expires. Logan is asked to find a group of Runners and has his own clock moved forward. When he realizes that he can't have his clock moved back, Logan decides to help the runners, including Jessica 6 (Jenny Agutter). Together, they flee Francis and fight Box (Roscoe Lee Brown), a cyborg who is freezing Runners looking for sanctuary. Once free of the domed city, Logan and Jessica find out the truth about their civilization and the knowledge that one old man (Peter Ustinov) has that can change everything.