In the summer of 1952, Joyce and Charlie Savigear are waiting on a railway platform in the quiet English countryside. The siblings have just been released from borstal to start a new life as apprentices at Leventree, an architecture practice with a difference.

The architects who've chosen them are Florence and Arthur Mayhood, a married couple motivated to give young offenders second chances. At first, they seem to offer the Savigears a steady path to happiness. But when a menacing figure from Joyce's past comes knocking, they are lured back to the world they left behind. Will the Mayhoods' goodwill be enough to steer their young apprentices away from danger, or will the darkness of their past catch up with them?