The captain of a merchant ship, Vasily Sedov, receives a radiogram with extremely unpleasant and even frightening content. It reports that on board his ship there is a particularly dangerous criminal who has committed a double murder and robbery of a cash-in-transit vehicle. True, the name of the villain is not mentioned in the radiogram. Sedov decides to find the criminal on his own, but does not have time to do so. The ship runs aground, and now there is no time for investigations. The crew hastily evacuates to the nearest uninhabited island. And only a few hours later, when the sailors come to their senses, it turns out that the second mate has disappeared without a trace...