Nancy invites friends Bess and George to go camping in the woods. Little do they know, Nancy has motive for the camping trip. Strange lights have been seen in the woods and Nancy wants to get to the bottom of it. When the girls see the lights, they run towards them and discover an old government factory no longer in use. Or so they thought. They enter the rundown building and meet Roy Hinkley, an engineer. He explains he’s there to find the hidden magnetic tank engine that can operate on 200 miles per gallon. Problem is, he thinks there is a ghost in the building trying to protect anyone from locating the tank. Nancy and her friends find themselves on the case looking for both the ghost and the tank. ( )