Three prisoners nearing the end of their jail sentences; 'Dodger' Lane, 'Jelly' Knight and 'Lennie the Dip', are visited by a vicar seeking to find employment for them. He is actually smooth-talking conman 'Soapy' Stevens, who proposes a large-scale diamond robbery. They will also have the ultimate alibi; they will break out of prison, commit the robbery and then break back in.