In this 12th book in the Key Mystery Series, Mandy, Nick and friends are working at an archaeological dig in an old river town in Maine. They are searching for artifacts from the 1814 Battle of Hampden which happened there in defense of the ship the USS Adams. As tools and artifacts disappear from the excavation, the children are determined to stop the sabotage. Meanwhile, on the grounds where the battle took place, they see the ghost...