While exploring the caves around Dragon's Mouth Cavern, a series of unusual and somewhat frightening events convinces the Alden children that someone does not want them around.

A rock slide strands the Aldens on a mountain! But being stuck on Old Flat Top isn't all bad. As the children wait for rescue, they discover that a secret cave has opened up-on that just might hold legendary treasure!

When the Alden children accompany their grandfather on a trip to Seattle, they discover clues throughout the city, seemingly planted just for them.

The Boxcar children travel to Maine, take canoes into the wilderness and live in a house exactly like the one on Surprise Island, except the Maine house is brown, not yellow. They untangle the mystery of the two houses.

Henry, Jessie, Violet, and Benny used to love alone in a boxcar. Now they have a home with their grandfather, and they're spending a week at Camp Seagull on beautiful Claw island. When they arrive at Camp Seagull, the Alden children look forward to a week of new friends, exciting activities, and most of all, the annual camp Olympics. But as soon as camp begins, Henry, Jessie, Violet, and Benny realize that someone is not playing fair. Everything...

Benny's friend accompanies the Aldens to the South Seas for a vacation on a supposedly deserted island where they find an unusual mystery.

The Alden children draw upon their resourcefulness to save the neighborhood firehouse from being torn down, while they also face a series of mysterious incidents connected with it.

The Aldens investigate when the new coach of their community basketball league has her Most Valuable Player trophy stolen.

The Alden children plan to ride in their boxcar at the Greenfield Founders' Day Parade, but the newly refurbished boxcar is stolen a couple of days before the big event.

The Alden family rents a houseboat to drift down the river, and encounters a mystery in the little towns along the river, involving a fast black car.