When a man selling leather goods door to door steals the key to their detective father's file cabinet, Frank and Joe Hardy set out to track him down. An odd mark on a key case which the man sold to their mother leads the teenage sleuths to an Indian village, whose chief begs them to help him. Two strangers have claimed title to the Indians land, the deed to which had been secretly buried by the chief's father, along with other valuable tribal possessions, shortly before he died. The only clue to the location is that a crisscross shadow marks the site when the October full moon is low in the sky. Recommended for ages 8 to 14.