A police officer in the future uncovers the deadly secret behind a society that worships youth.

It's 2274, and on the surface, it all seems to be an idyllic society. Living in a city within an enclosed dome, there is little or no work for humans to perform, and inhabitants are free to pursue all of the pleasures of life. There is one catch however: your life is limited and when you reach thirty, it is terminated in a quasi-religious ceremony known as "carrousel". Some, known as "runners", try to escape their fate when the time comes, and it's the job of Sandmen to track them down and kill them.

Logan (Michael York) is such a man, and with several years before his own termination date, thinks nothing of the job he does. Soon after meeting a young woman, Jessica-6 (Jenny Agutter), he is ordered to become a runner and infiltrate a community outside the dome known as "Sanctuary" and to destroy it. Pursued by his friend Francis (Richard Jordan), also a Sandman, Logan and Jessica find their way to the outside. There, they discover a beautiful, virtually uninhabited world. Logan realizes that he must return to the dome to tell them what he's found and be set free.