Slip, Sach, Whitey, Butch and Chuck witness a warehouse robbery, and are arrested and jailed on suspicion. Gabe Moreno, their lawyer-friend gets them released on bail. Since the charge of suspicion is one that the prosecutors appear to believe can be easily proved, the gang is awaiting trail, when Whitey, a short-wave radio fan, picks up information that leads him to believe that instructions for the warehouse robbery and others are given by an inmate in the penitentiary to his pals on the outside via short-wave radio. When the five go on trail, Slip and Sach plead guilty so that they may be imprisoned and the other three are given probation. Once in the Big House, Slip and Sach learn immediately learn that two notorious gangsters, Pretty Boy Gleason and Benny the Blood, expected to arrive at the prison have received a last-minute stay-of-sentence, so they decide to pose as Pretty Boy and Benny, in order to be readily accepted among the Cons and learn which of them is the one sending out the robbery instructions. They meet the leader, Bat Armstrong, and learn from Whitey, who has intercepted one of Bat's short-wave messages, that a prison break is planned. But before they can do much about that, the real Pretty Boy and Benny are imprisoned, and Slip and Sach are now known by Bat and his friends to be impostors.