When Septimus Similon, practising wizard, fourth class, makes a major discovery, he gets more than he bargained for. To disprove a fellow wizard's rule, he has enclosed a large area of Middlesex within a barrier which is impenetrable, immovable and permanent. For Alison and her classmate Kevin, that's bad enough - Alison's mum can't get home and Kevin can't leave - but somehow Sep has also mixed up this dimension with the wizards' world of Theromantia. Now Alison is being mistaken for Zelda - the enemy - and being hunted down, while puny Kevin is suddenly revered as The Ultimate Warrior. And dangerous creatures like the flying Thelamungus circle ominously. Someone needs to sort this mess out - but just where has Sep got to on his flying carpet...?