In the south east of France is a mountainous region of villages and sheep farms, where life is still lived the way it has been for centuries, and attitudes have barely changed. The invasion of wolves across the Alps from Italy is a source of fascination to the wildlife service and biologists, who observe their behaviour and track their movements with almost obsessive interest. One such biologist is a Canadian, Johnstone, who identifies totally with the wolves, giving them names and ascribing a personality to each, feeding rabbits to the one that is too old and toothless to kill his own prey.

Everything changes, however, when sheep are brutally killed, in what seems from the toothmarks to be an attack from a giant beast. A local woman believes that the perpetrator is a werewolf, but is herself killed the day after making the accusation. A hermit, Massat, vanishes - leaving behind in his hut a map that traces a twisting route through the region, including places where sheep have been killed.

Watchee is an old shepherd who worked for the dead woman, and Soliman is her adopted son, abandoned by a presumed African woman and a source of great strangeness to the locals. Watchee decides that Massat must be the werewolf: he and Soliman resolve to follow his trail to exact revenge. But they can't drive, so they persuade Camille, a musician, plumber and girlfriend of Johnstone, to go with them.

Most of the book describes the pilgrimage made by this odd trio up and down the rough, almost vertical tracks and hairpin bends of southern France in an old sheep truck, in which they live, sleep and eat. These idiosyncratic characters - never sentimental but nonetheless very appealing - share ideas about the crime, philosophise about their lives, and squabble about the best way to find their quarry - and what they will do when they find him.

The plot is completed by Commissaire Adamsberg, a policeman as idiosyncratic in his own way as the three "musketeers" wending their way towards a showdown with the person killing sheep and people. Adamsberg is himself on the run from a female putative assassin, but part-way through the book hooks up with his old flame Camille to help solve the mystery of the wolf-murderer. All four of these people contribute in their own ways to the final realisation of who is behind the crimes.

I've never read a book quite like this one. It is individual, charming and absorbing, yet certainly not "cosy" or twee - to the contrary, it is more often ruthless and unflinching. There is a dash of romance, wry humour, philosophy, plenty of detective work, strong characterisation and a satisfyingly original story, all wrapped up in about 250 small-format pages. A reader could want no more.