Mae Barlowe’s annual beach trip is anything but a vacation. It’s the anniversary of the worst day of her life. When her husband and best friend surprise her with a last-minute itinerary change in the form of a couples’ cruise, she struggles to hide her reservations about the new plan. A week spent cruising around in a tropical paradise sounds like a dream come true to everyone else, but for Mae, it’s an eerie reminder of chilling memories from her past. Once on board the ship, a mysterious stranger causes confusion among the group, leading them to ask unsettling questions of one another. Before they can get real answers, tragedy strikes. Trapped on the vessel as it ventures toward their first destination, the friends struggle to come to grips with their new reality.