Based on a true story, a group of allied escape artist type prisoners of war are all put in an 'escape proof' camp. Their leader decides to try to take out several hundred all at once. The first half of the film is played for comedy as the prisoners mostly outwit their jailers to dig the escape tunnel. The second half is high adventure as they use boats and trains and planes to get out of occupied Europe.

Frank Leone is nearing the end of his prison term for a relatively minor crime. Just before he is paroled, however, Warden Drumgoole takes charge. Drumgoole was assigned to a hell-hole prison after his administration was publicly humiliated by Leone, and has now arrived on the scene to ensure that Leone never sees the light of day.