The S. S. Arcturus sails from Shanghai to San Francisco, and Dr. Jim Craig takes the post of ship's physician in order to be near Ann Grayson, the ship's nurse. Chief Engineer 'Crusher" McKay also has his eyes on Ann, and this brings an immediate conflict between the two men. When an epidemic breaks out below decks, Craig tells McKay the engine-and-fire rooms must be put under quarantine, but all of Craig's efforts to keep the disease from spreading are opposed by McKay.

Su un piroscafo in navigazione sul Pacifico scoppia un'epidemia di colera. Il capo macchinista, irascibile e severo coi sottoposti ma in fondo di buon cuore, si prodiga per la salvezza dell'equipaggio anche a costo della propria incolumità.