The third book in the classic Hardy Boys mystery series! Join these amateur sleuths on an action-packed adventure as they work to solve the case before it's too late. With two cases in tow, the Hardy boys look to Turner mill for clues. Determined to learn the secret of the old mill, Frank and Joe employ a clever ruse to gain entrance, only to find themselves trapped. How the young detectives extricate themselves from this dangerous situation and unravel mysteries will keep readers tense with suspense!