China Passage (1937)

Tommy Baldwin and Joe Dugan are entrusted to carry a fabulous diamond. If they succeed, they will be well paid. If they fail, they will be well buried. When they go to pick up the diamond, there is a great gun battle, a cannister of knock out gas, and the diamond is stolen. The police round up everyone that they can find in the area and search them, but the diamond is not found. Strangely, everyone who was rounded up that night and released boards the steamship Asiatic the next day traveling from Shanghai to San Francisco. Tommy and Joe only have the trip to find out who snatched the diamond, and they suspect the seven people from the night before. But as the trip progresses, the bodies begin to pile up and the clues are few.