Once upon a time there was a teenager, called Lizzie, who had the most untidy bedroom floor. Ever. Under the mattress on her bed, there was a sandwich, that had been there so long, it had become a unique life form, black, slimy and malevolent. Naturally, Auntie Lizzie does not like her room being looked at, so she keeps it locked. Until one day, her niece Erin finds the door open and ventures inside. A sudden sting on her finger shrinks her until she is tiny and leaves her frightened and alone on the bedroom floor, where she has to make new friends and fight off unexpected dangers and enemies until she discovers the real reason she is there and the terrible task that faces her.