Ever since Al Capone built Happyland Amusement Park in the 1930s, treasure hunters have believed Capone's lost fortune awaits somewhere at the end of a hidden ride no one has ever found, until tonight. When Henry finds a set of blueprints leading to the loot, he recruits his best friend and big sister on the quest. The kids quickly find themselves on an incredible adventure when they sneak into the abandoned park and witness it's attractions magically come to life.