S.S. MurderCub reporter Mary Llewellyn is on a soothing sea cruise to help her recover after a minor operation. Her fellow passengers are pleasant enough, gathering to play a friendly game of bridge to pass the time. But the game turns considerably less so when a wealthy businessman samples a cocktail and ends up dead at the table. The news that someone onboard dumped a fatal dose of strychnine into the man's drink sends a ripple of panic through the voyagers.