Hardy Boys 31: The Secret of Wildcat Swamp - The Hardy Boys New edition

An invitation from Cap Bailey, science teacher at Bayport High, to accompany him out West to Wildcat Swamp on an archaeological expedition triggers off a series of dangerous events for Frank and Joe Hardy. - - Just before they leave, a ruthless criminal breaks out of prison. Their famous detective father, who is tracking down a gang of freight-train robbers, suspects the escapee is part of the gang. Investigation leads him to believe that the robbers might be hiding out in Wildcat Swamp!

On their way West the boys and Cap have a near-fatal accident in a private plane which has been sabotaged. When they start digging for fossils, a giant boulder comes hurtling straight toward them as if guided by an invisible hand. Though warned to leave the area, Frank, Joe and Cap doggedly remain until they have caught the cunning ex-convicts they are up against in the swift-paced adventured.