When Matilda Benson solicits the help of Perry Mason, her request seems simple enough: cruise to a gambling ship moored just beyond the twelve-mile limit and buy back the IOUs signed by Miss Benson's niece. But after Mason reaches the floating casino, he discovers problems aplenty--most notably the ship's owner with a bullet hole through his head.
Strangely enough, Matilda and her niece are also on board that night . . . when someone tosses a gun over the railing. Does Perry Mason's client have something to hide? With the support of his trusty secretary, Della Street, and the ever-helpful Paul Drake, Mason dives into an ocean of menace.