Frank and Joe Hardy become suspicious when their friend Chet Morton enrolls in a summer school that sounds too good to be true. While investigating a burglary at the Seneca Indian Reservation in New York State they also investiate Zoar Collage which happens to be nearby. Their sleuthing leads them to believe that there is a connection between the professors of what appears to be a fictional collage and the theft of a tribal mask titled Spoon Mouth. This mask was created when some melted coins happened to look like a sacred Indian image. Now it is missing and the boys' investigation proves to be dangrous however they successfully recover the mask and capture the thieves.