Previously published in the print anthology The Regatta Mystery and Other Stories.
Diamond merchant Isaac Pointz and his guests come ashore at Dartmouth to enjoy the fair after the yacht races. Over dinner, young Eve Leathern bets she can make Pointz's famous diamond, the Morning Star, disappear right at the table. When the girl does exactly that, she discovers she has made the priceless gem disappear more completely than she had intended. Fortunately, Parker Pyne is able to get to the bottom of what really happened to the Morning Star.