The Queen's jewels.

Jessica Fletcher has always wanted to take a transatlantic voyage on the legendary Queen Mary II. Now, she's finally getting her chance. She's hoping to fly to London, spend a few quiet days visiting, and then depart on the high seas. When she calls her old friend, Scotland Yard Inspector George Sutherland, to let him know she's on her way, he mentions the case of an enormously valuable diamond that was stolen from its wealthy owner, who was murdered during the heist. Jessica is well aware of the story. But when she finally boards her dream ship, the deadly mystery appears to have followed her up the gangplank. Now, in the middle of the Atlantic Ocean, she must try to enjoy the sumptuous seaborne surroundings while she tries to find a priceless diamond-and the killer desperate enough to take a life for it.