The Godfrey family is vacationing on the North Atlantic seaboard. One dusky evening, Rosa and her uncle David get into an argument about her secretive romance with one of their guests, John Marco. That's when a man with a .38 revolver emerges from the twilight. When Ellery Queen arrives, looking forward to a summer getaway on the coast, he realizes his trip will be no walk on the beach. Rescuing Rosa, he discovers her captor mistook David for John and struck the former down instead. But Ellery has more work to do when Rosa's shady sweetheart is found dead. There are plenty of guests and members of the household who might have wanted John dead, but who did it?