When Jaine takes a teaching gig on a fancy cruise ship heading for the Mexican Riviera, she’s hoping for a week of fun in the sun and hanging out at the all-day buffet. On her first night at dinner, she’s seated beside Emily Pritchard, a sweet, wealthy 70-year-old whose financially dependent relatives don’t take kindly to Emily’s blossoming relationship with the ship’s smooth-talking British dancer, Graham.

Within days, Emily announces her engagement — but next morning, Graham is found dead on deck. The captain is quick to accuse Graham’s former girlfriend, but Jaine suspects there are more sharks lurking about. And with Jaine’s flirtation with Emily’s handsome nephew further more complicating matters, her relaxing cruise is about to encounter some very treacherous waters…