Eleven-year-old Maxwell is always, always in trouble. Roaming the town with his beloved pet dog Monster (who he rescued as a puppy from being run over) as a way to escape his parents' constant sniping at home, he's a menace to the neighbours and teachers at school. While visiting an elderly neighbour, Maxwell comes across a mysterious cabinet of curiosities and suddenly finds himself erased from his life: it's as if he's never existed. Able to walk around anonymously might be great at first - finally, no-one is yelling at him! - but he soon realises that he misses his old life and, crucially, if he had never existed, then he wouldn't have swooped in and stopped Monster the dog from being hit by that car... Maxwell needs to find a way to reverse his erasure, with the help of his best friend Charlie and his sister Bex, who need a whole heap of persuading that this weird kid they've never clapped eyes on is actually super close to them in his former life...