There was a time when you could set your clock by it. All the familiar Harry scenes have gone missing, from the inaugural, always comforting comedy inside No 4 Privet Drive and the annual bullying bout on the Hogwarts Express, to Mrs Weasley's Christmas jumpers and - more mercifully - Hagrid's inevitable adoption of some tiresome magical creature whose assistance will later prove critical.

But some regular readers may also be disconcerted by a tranche of Hogwarts in which there is neither Quidditch nor lessons. In earlier volumes, Rowling made heroic efforts to initiate new readers, but since this process would now require, at a minimum, a glossary, rule book and catalogue of magical objects, she seems to have given up the task as hopeless. To anyone unacquainted with the epic so far, the latest tale will be incomprehensible. Now that the 17-year-old Harry has abandoned school for his dreadful, extramural quest, only he can determine whether the lights will go out all over the democratic wizarding world. By book seven, if you are familiar with Rowling's vast, ever-expanding parallel universe, it seems only to be expected that this wizarding terrorist should, by now, be close to completing a fascist-style takeover of the UK (both material and magical sections), in the course of which non-wizards and half-wizards are being rounded up for questioning by 'pure bloods' and sent off - if they survive their show trials - to a wizard-run concentration camp. With JK Rowling it has generally been niggling little questions of internal logic that give the reader pause, rather than the mysteries of her grander scheme in which that prime specimen of embodied evil, Lord Voldemort, slowly acquires the power he needs to defeat Harry Potter, his only adequately qualified adversary.

It cannot be giving anything away to reveal that we never discover how Eloise Midgen can be a martyr to acne at Hogwarts, a place where bones can be grown back and complex orthodontics effected with the wave of a wand. There are still one or two questions left unanswered at the end of Harry Potter's last adventure.

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