The two previous volumes have seen Harry Potter enrolled at the Hogwarts School of Witchcraft, away from the clutches of his repulsive, pantomime- nasty uncle and aunt. In Harry Potter and the Prisoner of Azkaban, our hero, now in his third year, faces new dangers from an escaped mass murderer. This is nothing new: terrifying monsters are always trying to kill Harry, whose mysterious crescent-shaped scar on his forehead marks him out as a serious threat to all forces of evil. But with another four adventures planned after this, there is never any real possibility that he will be rubbed out along the way.
Even so, the threats that confront him and the last-minute escapes whistled up when all seems lost remain as gripping as ever. Despite the constant melodrama, these are not neo-Tolkienesque stories full of pompous Dungeons and Dragons-type rodomontade. The distinctive and winning feature of JK Rowling's writing is its inventiveness and good humour. In this book, images in photographs wave back cheerily at onlookers; mirror reflections converse with their originals; and animals in pictures move from one frame to another in search of better pastures.
Descriptions of lessons - normally omitted in school stories - play an important part because, for once, they are so interesting. There is tuition in how to read tea leaves, make a shrinking solution or tame a boggart. Shopping trips to the local village realise nose-biting tea-cups, levitating sherbet-balls, blood-flavoured lollipops - for vampires only - and exploding bonbons.
All this takes place within the tried and tested boarding-school story formula, which Rowling has single-handedly rescued at a time when it had collapsed under the weight of its own former snobbery. The boys and girls at Hogwarts remain satisfyingly exclusive, but due to their magical talents, not their money or influence.
Except, that is, for a few sportingly villainous pupils, whose sneers and attempted put-downs are always beaten off with relish. The strengths that once made boarding-school stories so successful remain: a gratifying absence of fussy parents; house rules that can be broken without incurring guilt; a limited cast of characters set in one building that soon becomes familiar; mean teachers with mean-sounding names ("Severus Snape"); and best friends and bullies. Most traditional of all, each tale features a final house match and the vital winning of the school cup. But this doesn't involve cricket or rugger but quidditch, a magical game played on flying broomsticks. This is so convincing it is as if the planned film version, with all the necessary special effects, has already been screened.
One temptation in any successful series is to keep repeating the formula in a timeless vacuum that allows characters to stay the same age while continually celebrating the arrival of new birthdays, Christmases and summer holidays. Harry Potter is different. Not only does he age with each book, but now shows the first, faint stirrings of interest in the opposite sex. Yet, tactfully, this new orientation is never allowed to get in the way of the next alarming adventure.
Harry is both hero and anti-hero. Brave at heart, he has a knack of getting into waters too deep for him to manage alone. Sometimes he is faced by moral uncertainty as well as physical danger. A Cinderella-type orphan, his longing for his parents - killed by the same dark spirits out to eliminate him - is poignant. Very much a modern figure, he battles with weakness rather than glories in personal strength. Bespectacled, a drudge at home, he is easy to identify with, particularly for young readers.
But how resoundingly these are compensated for when Harry finally triumphs, as he always does. These 317 pages of highly paced narrative show every sign of continuing to mesmerise readers of both sexes, and all ages. Harry Potter represents a considerable gift to a government intent on raising reading skills. David Blunkett should award the author a broomstick medal for services to education. She may, after all, have done as much as every literacy hour rolled together to introduce a new generation to the joys of reading for its own sake.
The reviewer teaches psychology and children's literature at the University of Sussex