The Aldens are preparing for a yard sale when they find an old wooden mask. Violet notices that the mask looks like a Native American mask that she had read about. When the children go to the library to learn more about the mask, they discover that it belongs to the Hopi tribe. The children plan to deliver the mask to its rightful owners.

But Henry, Jessie, Violet, and Benny soon find out that they’re not the only people interested in the history of the old wooden mask. A strange man is following them around, and an antiques dealer is looking for more than her fair share at the Boxcar yard sale. When the mask is stolen from their garage, the Aldens vow to find it as soon as they can. But will they be able to recover the mask with such little evidence?