The adventures of the four Alden children as they investigate a mystery that took place in the yellow house on Surprise Island many years before.

When the Aldens spend the summer riding on a train, they get to live in a train car once again - this time, they're staying in Caboose No. 777. The number is hard to forget, and indeed, the children meet people at each stop who seem to know it well. It turns out Caboose No. 777 has an unusual past - one that comes with its very own mystery!

The Alden children, snowbound in a vacation cabin, discover adventure in surrounding wild life, three children they find in the snow, and a search for a lost recipe.

Because they do not want to be separated, four orphaned children run away and live in an old abandoned boxcar

Despite warnings and threats from a woman named Angela, the Boxcar children set out on a canoe trip with Aunt Jane and become involved in a case involving a mysterious riddle and a stolen coin collection.

The Alden children suspect that the other guests are somehow involved when things begin to disappear where they are staying in Washington, D.C.

While investigating the disappearance of Mr. Woods' beloved cat, the Alden children uncover a number of mysterious suspects in the catnapping

When the Aldens go to the Pickering Natural History Museum to assist with the opening of a dinosaur exhibit, their work is hampered by a series of mysterious happenings.

While visiting Lake Lucille in the Adirondack Mountains, the Aldens hear stories about a monster in the lake and then encounter evidence that it may be real.

When a professional hockey player comes to Greenfield with plans to build an ice skating rink, the Alden children suspect that someone in town wants to stop the project.