When the Aldens go to dinner at a local Chinese restaurant, Benny can't wait for his favorite part of the meal—dessert. He loves breaking open the delicious fortune cookies and reading the messages inside. But when Benny opens his cookie, instead of a fortune, he finds a handwritten riddle! One cookie leads to another, and the Aldens soon realize they've bitten into another mystery. Who is leaving the Aldens the mysterious cookie clues, and why?

The Alden's neighbor, Lina, thinks there's treasure hidden in her attic and she wants the Boxcar Children to help her find it. Of course, the children are eager to help search—but it appears they aren't the only ones looking for the treasure. Can the Boxcar Children discover the treasure in the attic before someone else finds it first?