No Man's Land.

Free and easy Garrett Cope loves Katherine Gresham, but his rival, Henry Miller, who is really Heinrich Mueller, a World War I German spy, gets rid of Garrett by having him arrested for the murder of Pembroke Van Tuyl. While Garrett is in prison, Katherine marries Mueller, but Sidney Dundas, knowing that the German actually committed the crime, finally confesses, and Garrett is freed. Meanwhile, Mueller takes Katherine to a remote island called No Man's Land, which he uses as a base for blowing up Allied ships.