Henry, Jessie, Violet, and Benny are going on a cruise with their grandfather in the Caribbean. They discover all kinds of fun things to do--swim, explore every inch of the ship, eat lots of delicious food, and visit the islands where the ship docks. They become fast friends with a man named Max. That's when a lot of strange things begin go happen. Max needs to send a message back home, but the phone lines become disconnected. Then the ship gets stalled because of engine trouble. Will the Boxcar Children be able to discover who or what is the cause of all this? Will they be able to help their friend Max in time?