The Mystery of the Stolen Dinosaur Bones
by Gertrude Chandler Warner
The Aldens are visiting a real dinosaur dig in Montana, in an area full of fossils and caves! But the bones of a rare dinosaur have gone missing, and when the children begin to search for clues they hear strange noises in the caves and discover mysterious tracks! Why are bones disappearing? And could there be a real-life dinosaur on the loose?