"The Alden children are fixing up an old castle that will be turned into a museum, but they have to solve the mystery hidden within the castle's walls"--

After the Alden siblings visit their Great-Aunt Jane's ranch in a mining town, there is a mysterious fire which damages three houses, but Benny's friend Mike notices a strange man in a blue hat in the paper and Mike and Benny suspect he may be the culprit.

"The Alden children are helping their new neighbors build a tree house when they discover an attic window that not even their neighbors knew about"--Title verso page.

"The Aldens visit their old friends, the Piccolos, at their pizzeria. When they learn the restaurant isn't doing well, they offer to help. But the oven doesn't work, the electricity shuts off, and then someone hands out fake coupons! Who wants to shut down the Piccolos' Pizzeria?"--Back cover. When their favorite pizza restaurant almost goes out of business, the Alden children try to help their friends stay open while they find out who is behind...