An engineer is wrongly convicted of selling secrets to enemy agents and is sentenced to life in prison. Convinced it was his former partner who framed him, he enlists his son to investigate.
John Richards (Jack Gwillim) is sentenced to life in prison for treason. 15 years later his ailing wife convinces their son Jim (Francis Matthews), a law student, to visit him there for the first time. John proceeds to proclaim his innocence, of being falsely accused of stealing plans for a new periscope in wartime. Jim is shaken by his father's claims, and so accepts his mother's death wish to learn the truth. He investigates his father's ex-partner, Ralph Thomson (Basil Dignam), and using an alias, makes the acquaintance of his daughter Sue Thompson (Jill Williams). They end up becoming romantically involved. Then Ralph's brother, Edward Thompson (Mark Singleton) comes into the picture and uncovers Jim for who he really is. Ralph breaks this heart breaking news to his daughter. Meanwhile Edward sends thugs to break Jim's will to keep on investigating. As luck will have it, the thugs do their thing just as Sue is breaking up with Jim, both get worked over, and so she takes Jim's side again. They go to pursue a secretary who holds the secret to the truth, and this leads to the gran finale with the villains. Need I say more?
