The mystery girl: Henry, Jessie, Violet, and Benny are working in a general store to heal out a friend of Aunt Jane's. The girl who works in the store is behaving strangely, is nervous, and won't answer any questions. Then a strange man comes to the store asking about her. The mystery cruise: The Aldens are on a cruise in the Caribbean when things begin to go wrong. The ship's radio breaks, there is a false alarm about someone falling overboard, and there is engine trouble. Is someone deliberately tampering with the ship? The disappearing friend mystery: The boxcar children decide to raise money to help the hospital by forming a service called the Boxcar Helpers. They babysit, wash cars, mow lawns and care for pets. But Beth keeps disappearing, and things keep going wrong. Is someone trying to put the out of business?