Foul Play in Funland

While digging for clams on the beach, the kids see that their favorite boardwalk amusement park Funland suddenly light up and all the rides come to life, even though it is the off season. When they investigate, the start seeing a strange man with super-human strength and speed running throughout the park. They investigate to discover who the man is, and why the brother and sister who maintain the park keep insisting that it isn't open, and no lights or rides are operating.