The Return of Sophie Lang.

In order to give up her life of crime and go straight, renowned jewel thief Sophie Lang fakes her own death and retires to London. She soon finds a job as a companion to a wealthy old lady who is also a jewel collector. One day her employer decides to take an ocean trip to the US, taking Sophie with her. She also takes along a $200,000 diamond, which she locks up in the ship's safe. Of course, the diamond is soon stolen from the safe. A reporter also happens to be aboard the ship, and he has had his suspicions about who Sophie really is. Sophie has to find the real thief and recover the jewel before the ship docks in New York, because an investigation could reveal her true identity.