Mona Moon and her new husband, Robert Farley, Duke of Brynelleth, are on their honeymoon at last. They have just boarded the RMS Majesty ocean liner. The couple are looking forward to visiting Robert's ancestral English home, Brynelleth, and then off to Paris before winding up on the Italian Riviera. After a romantic evening of dancing until the wee hours of the night, Mona and Robert discover their suite has been ransacked and Mona's jewelry, supposedly secured in their stateroom, has been stolen.
Mona is horrified, as some of the jewelry belongs to the Brynelleth Estate and were cherished pieces of Robert's mother. The ship's crew searches the ocean liner, and a gold brooch turns up in a bartender's cabin. It is the same bartender who served Mona earlier in the evening. The only problem is the bartender has been murdered and the rest of the jewelry is still missing.