Jimmy wants to prove his investigative skills to his father and so boards the Jennings pretending to be Charlie Chan, with his younger brother Tommy (Layne Tom Jr.) in tow.

The ruse doesn't last long and soon the real Chan arrives on board, interrogating a motley assortment of crooks, heiresses and crew as he works to solve a crime whose only witness is secretary Judy Haynes (Phyllis Brooks).

Captain Johnson is eager to unload his cargo, which is mostly a shipment of "big cats" destined for the San Francisco Zoo.Deckhand Al Hogan is fond of walking his pet lion Oscar on the main deck, to nobody's pleasure.

Jimmy starts a "controlled fire" on the ship, hoping to panic the killer in grabbing the hidden money and making a run for it.

We close with the remaining passengers gathered around the ship-to-shore phone, listening to the coos and cries of Charlie Chan's first grandchild.