The Bad Book Affair, By Ian Sansom

"What am I doing here?" might be the perennial cry of Ian Sansom's protagonist: bemused but doughty, London-born, Jewish vegetarian librarian Israel Armstrong. "Here" is the backwater of Tumdrum, an imaginary, generic town on Northern Ireland's northernmost coast. What Israel is doing, by and large, is dispensing books to more or less reluctant readers from an inadequately equipped van – the "mobile library" of Sansom's sportive series.

It also falls to Israel's lot to do a bit of investigating. In The Bad Book, this time it's a schoolgirl who has disappeared, the daughter of a flashy local Independent Unionist politician named Maurice Morris. Where is Lyndsay Morris, the amateur goth? Why is her mother strangely unperturbed by her daughter's absence? And is Israel somehow responsible for the whole thing by failing to censor the schoolgirl's borrowing? There's an "unshelved" selection of books unsuitable for juvenile reading, and Lyndsay has gone off with one of these tucked under her arm: Philip Roth's American Pastoral.

Israel lives in a converted chicken coop, his girlfriend has left him, he's about to turn 30, his only kindred spirit in the neighbourhood is polished off by a shelf of falling books, and some comic-sinister policemen are on his trail. He can't even indulge in a bit of a depression undisturbed. And he's engaged in a running battle with his Chinese employer Linda Wei over questions of terminology. In Israel's book, a library is a library, not a "Mobile Learning Resource Centre".

With the help of his ally, Ted the taxi-driver, of a peculiarly Ulster lugubriousness and aplomb, Israel picks up a clue and follows it to a conclusion, encountering along the way a whole galère of local oddballs and creeps, including religious creeps. For all its "mystery" aspect, The Bad Book Affair is, like its predecessors, less a detective novel than a work of humorous social observation, by turns astute, hilarious, wry and rueful. What it lacks in intrigue it makes up in clarity of style, and is engaging and diverting throughout.