Cheerilee starts seeing a door that follows her about. It appears in strange places, such as on a thin fence or on the roof of her hotel room. She thinks it's merely an accident of entertainment magic in Las Pegasus at first, and pays it no mind.
Later, she realizes she can actually enter it, and it takes her to new and strange places. It isn't so bad at first, but when her new friend cannot enter it without, and she takes him through, things go bad, and Cheerilee learns things aren't as they seem.