I'm not a fan of book reviews that give the game away, belching out plot-spoilers like fur balls, but in the case of Matt Haig's To Be A Cat you'd have to be a bear of very little brain not to get what's going to happen, before you've even turned to the first page.

There is, of course, the title itself, To Be a Cat, reminiscent of Floyd Huddleston and Al Rinker's "Ev'rybody Wants to Be a Cat" from Disney's animated romp The Aristocats, though Haig's book has the strapline: "Imagine what it would be like " preceding the title, rather than "Ev'rybody Wants  "If that weren't enough, there's a picture of a curly-haired boy turning from human to cat in four stages (rather like one of those evolutionary timelines of Man from stooped hunter-gatherer to Wall Street banker, only more positive). On the back, beneath a Eadweard Muybridge-style sequence of a black cat in motion, is the single line: "Be careful what you wish for "

As Lloyd Grossman used to say, let's look at the evidence. The conclusion? That we're about to embark on an adventure with a boy not being careful what he wishes for and turning into a cat. So, although the transmogrification  Haig refers to it as plain old metamorphosis, but I think he missed a trick there  doesn't actually happen until page 60, the cat is out of the bag from the very outset.

The boy in question is Barney, whose father, Neil, mysteriously disappeared the previous summer after he and Barney's mum had divorced. "He just vanished. Zip. Poof. Gone. Not a trace."

Barney doesn't fit in at school. Neither does his friend, Rissa, but the difference is that she "was one hundred percent bully proof  She genuinely didn't care what people said about her." She lives on a barge without a TV.

Characters in To Be a Cat often have names to suit their personalities: the Primm twins are neatly dressed and every teacher's favourites; Gavin Needle  the school bully and a key player in this tale  needles Barney mercilessly; Mrs Lavender is the nicest teacher in school. Another key character is the "author" himself. (If not actually Matt Haig, that's how he signs himself at the end.) He's not a participant in events but his voice is a real presence throughout.

Two of my favourite characters, though, are the wonderfully rude head teacher, Miss Whipmire, who obviously hates children, and Barney's dog, Guster. Miss Whipmire has a cat-skull pencil pot on the desk in her study. Guster doesn't recognise Barney in cat form. ("Confine your tongue. Do you know who you're talking to? I am a King Charles Spaniel  ") Both make Barney's cat life difficult, in very different ways.

This is a fun book, but certainly not silly, and things really do get a little hairy once in a while: there's a whiff of real danger. And when Barney does become a cat, something very unexpected happens and, no, I'm not going to tell you what. It transpires that there are three types of cat: the two-legs (who used to be human); the firesides (happy, domestic cats); and the swipers (tough street cats). They don't all see eye to eye, of course. Then there's the mysterious Terror cat to contend with. Ultimately, though, To Be a Cat is a book about being comfortable in your own skin rather than someone else's fur.

 Philip Ardagh's Eddie Dickens Trilogy is published by Faber.