In January of 1962, 29 East Berliners escaped to West Berlin via a tunnel they had dug beneath the Berlin Wall, led by Erwin Becker, a chauffeur in the car pool of the East Germany Parliament, who served as technical adviser on this film. The film opens with Karl Schroeder (Don Murray), chauffeur to an East German Major, seeing a friend killed as he tried to drive his truck through the wall, He is persuaded by the friend's sister, Erika Jurgens (Christine Kaufmann), and his own family to engineer an attempt to make an escape to the Western sector of the city by digging a tunnel under the wall which is close to their home. Their efforts to evade the suspicions of the East German police, their fear of betrayal by inquisitive neighbors and the exhaustion of the digging are only a few of the difficulties faced by the group.