Millie Sanders has settled into her new position as assistant cruise director of the Siren of the Seas and is loving every minute of the adventure and excitement. A fresh wave of passengers have just boarded, and as the deck party gets into full swing, a frantic cry of man overboard is shouted over the loudspeakers. Millie rushes towards the crowd that has gathered on the portside upper deck and watches in horror as the ship's crew desperately tries to save a young man who has just gone over. Onboard investigators believe it's a clear cut case of vacation suicide, but Millie isn't convinced. Her suspicions are confirmed when she discovers the fiancé of the poor deceased man received a threatening note. The mystery deepens and the list of suspects grows when Millie discovers some of the friends who boarded with the young couple may have had reason to push him over, and that is just the beginning!