This book finds Arty and his new friend Little Hawk, an Apache, back at the line shack Arty discovered in the previous book. This time, however, the shack isn't deserted. Little Hawk has been living there. Before long, though, someone else moves in while Little Hawk is away. These unwelcome guests prove to be looking for more than shelter; but Arty, Little Hawk, and the Circle A hands are ready for them.