[1] After unmasking a clever jewel thief for the benefit of his police inspector father, Ellery Queen and his friend Judge Macklin leave for what they hope will be a bachelor vacation on the California Coast.

When the grounds are searched, the dead body of society sponge John Marco is found on the patio, garroted to death some time ago and wearing only a bathing suit.

Boston blueblood Leslie Court is then killed in his upstairs room even though he had been out of their sight for less than 15 minutes and all of the suspects were downstairs and their movements accounted for.

Uncle Dave had been living on the "missing" yacht, and swam ashore at high tide time each night to commit the murders.

Queen opines that while the first murder was committed for money, somewhere along the line Uncle Dave's mind snapped and he became a thrill killer who was even willing to kill the niece he loved.