In French Indochina, a magistrate is assigned to investigate the murder of his boss. Unknown to him, the boss had a policy of requiring the wives of his subordinates to sleep with him if they wanted their husbands to get promoted. What he also didn't know was that his wife was in the boss' office when he was killed. Complications ensue.
The ship-owner Herr Reeder Roberts organizes a world trip on his luxury liner "Yoshiwara". Aboard are millionaires and famous artists, but also criminals. The manager of the ship-owner, Stefan Martini, has been murdered shortly before the departure in a mysterious way. Several persons are suspected and these are, precisely, the passengers of the "Yoshiwara".
A doctor who cannot figure out what is wrong with his patient refers him to a detective, whom he hopes will be able to discern the cause of his mysterious illness.