Henry and Emmy Tibbett have been traveling and are now headed back to England, on the ferry out of Harwich. It's a trip Emmy has been looking forward to, but her excitement flags when it becomes clear that the cabins are all spoken for, she and Henry will have to bed down in the "sleeping lounge" with a motley collection of their fellow travelers. By morning, one traveler has lost both his life and his fortune in Dutch diamonds. That's bad enough, but a few days later, when Emmy's unpacking at home, she makes a discovery that puts both Tibbetts in real danger. It will take their combined analytical skills to get them free of that terrible boat ride.