The Coincidence Engine, By Sam Leith

Alex Smart is a PhD maths student who takes a road trip across America to propose to his sweetheart Carey. Smart is clueless. For example - and most importantly - he doesn't know that there are no less than four investigative agents on his tail. Two are from an arms and security company, while the other pair work for the Directorate of the Extremely Improbable, an agency involved in the paranormal.

They are all after a mysterious device which might have been invented by a reclusive mathematical genius and could be in Alex's possession. As Alex drives onwards, bizarre coincidences begin multiplying. Every narcoleptic in Mississippi falls asleep while crossing the road, while every shop in Alabama sells out of Chicken & Broccoli Rica-A-Roni.

This is a novel of ideas; literally so, because it is based on the conceit that an idea could become a self-directed entity in the material world. More specifically, it looks at the consequences of creating a machine that generates coincidences. If this is a scenario to make readers nervous, wary of whimsical self-indulgence or portentous post-modernism, fear not. Sam Leith pulls it off with admirable imaginative stamina, helped along by sharply observed and entertaining writing.

He has an eye for detail, often deployed on the minutiae of life across the pond, not least junk food. A way with simile and hyperbole is also evident. A youthful policeman's Adam's apple "bobbed up and down his neck like a fisherman's float after a motorboat has passed". Similar verve is on offer when it comes to characterisation. The head of the DEI, the Red Queen, is formidable: imagine a brutally acerbic Stella Rimington (though, teasingly, Leith never reveals the spook's gender).

Where he stars, however, is in his descriptions of mental conditions and madness (heavily mining, no doubt, his career in literary journalism). Banacharski, the brilliant mathematical sage who has apparently gone loopy, is a striking creation, from his rambling letters on legal paper complete with triple underlinings to his dietary preference for soaked nettles. Leith draws upon the real story of the mathematician Alexandre Grothendieck, but there's more than a hint here of a satirical take on the Unabomber.

Equally memorable is DEI agent Jones, who is psychotic. This means that he has no imagination and cannot extrapolate from real objects to imaginary ones. As a result he lacks any expectations or desires about the future, though he does not live entirely in the present.

Leith does toss conundrums about the universe, solely to see where they will land with maximum comic impact. This is a manic yet paradoxically well-ordered tale, in which coincidence intervenes to secure loose ends in a satisfying fashion.