David Almond has always had his eye on the marginal, the defeated, the odd, the off-key. Finding mystery in the boring, magic in the down-to earth, he has the startling knack of conjuring the uncanny out of the stuff that everyone else passes by without a second glance. His new novel for younger readers is both typical and different: the story of a lonely boy who runs away, and a knockabout comedy written in a cheerfully throwaway style, short on subtlety but big on laughs and fun.

It is all, quite literally, a fishy business. When the shipyards close, Stanley Potts's Uncle Ernie turns his house into a fish-canning factory ("Potts's Spectacular Sardines, Potts's Perfect Potted Pilchards") and Stan becomes his drudge. A brief period of homemade-machine mania is mercifully brought to an end when Stan visits a travelling fair and wins 13 goldfish. He is "entranced" (a fact formally confirmed by the fair's Gypsy Rose) by their "panting mouths and their delicate scales and their tender dark eyes". And when Uncle Ernie's madness takes a turn for the worse and attracts the attention of DAFT ("Departmint for the Abolishun of Fishy Things"), Stan has a circus to run away with, where he begins a promising career on the Hook-A-Duck stall. What he doesn't anticipate is something altogether grander and madder. Not just a career, but his destiny! Apprenticeship to the celebrated Pancho Pirelli  the man who swims with piranhas.

Almond has produced a circus ride of a story, with thrills and spills and all the fun of the fair. There are glittery prizes to be had, and big fat morals printed in coloured letters ("the little troubled runts are often the ones that turn out to be best of all"), as well as quiet moments in the silvery moonlight. Generally the pace is hectic (quadruple verb-clusters a speciality) and the action bold.

There's no lingering over refinements such as motives or ramifications and the storytelling voice is big-hearted with a decided preference for cheap and cheerful clichés. The characters are cartoonish (such as Gypsy Rose, the dastardly villain Clarence P Clapp of DAFT, or the policeman whose talk is full of "I know lads like you" and "Go on, get going"). They talk funny, and show a marked tendency to farce: the thugs of DAFT are much more Keystone Kops than Child Catcher. Like the fairground setting or the run-away-with-the-circus storyline, they're kitsch, completely unpretentious and fun to play with. The end of the story is cheerfully strewn with loose ends and the invitation to finish it (and some of the characters) off yourself.

Is it a success? For me, its freewheeling style disguises some difficulties. The opening fish-canning factory section, which seems a perfect fit with the swimming-with-piranhas ending, has a demented tone and pitch that is out of kilter with the rest of the book. The incompetent DAFT bunch seem unable to locate their proper role. The story has magic but lacks danger or fear. But the author's generosity of spirit saves it. There's no mistaking the hallmark Almond tenderness and the willingness to work with the common things of life, which animate it from start to finish and make it good.

Simon Mason's Moon Pie is published by David Fickling.