 Superman is forced to solve a mystery after Jimmy Olsen is abducted. A man aboard a ship to Metropolis has registered under a woman s name. Another man attempts to force him away. But the passenger kills the other man. The passenger then dresses up as a woman. The passenger, in an attempt to fool his pursuers, gives Jimmy an empty box. Thugs dressed as ambulance attendants kidnap Jimmy while the passenger gets away. The thugs are in the employ of a doctor. The mystery leads to Germany. Superman flies to a U.S. base there, where Clark Kent knows a Colonel. It turns out that radium has been stolen and hidden in earrings. Superman must fly back in a hurry to the U.S. to capture the passenger and the doctor.