This is a classy, stylish and troubling thriller from a writer who has over the course of his two previous novels proven he knows how to balance page-turning appeal, great writing and thought-provoking ideas. Before it was Amsterdam, then Greece; now Sherez turns his attention to his home town of London and comes up trumps again - for residents there are the familiar little places and moments that don't make it often enough into novels, and our daily paths are recast with those things from the dark end of the street that we might more happily turn away from. It's a tale, amongst other things, about the experience in the capital of African immigrants, refugees of small wars most of us hardly know about, young men trained to kill in places of heat and light and then set adrift, futureless, in an alien culture: "an unseen army living their lives under the radar, a shadow London of hospital cleaners, dishwashers and street sweepers. A city he passed every day yet never noticed. Invisible because they wanted to be, invisible because we preferred them to be so."

Detectives Carrigan and Miller hunt the murderer of a young Ugandan student through this squalid and sodden city (it's mostly raining, the best its inhabitants can hope for a break enough in the downpour to light another cigarette) while coming to terms with the low-key chaos of their own lives. The first in a series, we learn that Geneva Miller is the daughter of an émigré mother and going through a bitter divorce; Jack Carrigan is rather mysteriously widowed and haunted by decisions made on a post-Uni trip to Africa that left one of his best friends dead. Cautious at first, cast against each other by their commanding officer, slowly they begin to understand each other's silences and wounds in a way that bodes well for the novels to follow. Both their careers are heading in the wrong direction, and as much as anything the book is about reaching a certain point in life - a certain fatal distance from the halcyon days as an undergraduate - and realising that finally your options are much fewer, that some choices you've made really do count forever. There's a sadness to the core of the book, a loneliness, that gives this story a real charge: behind the twists and turns and surprising revelations, there is a sense that something really is at stake here, beyond the desire of the detectives just to solve the case.

With just the right balance between the classic and the modern - the currents of London's lost rivers and the data streams of Facebook and Twitter flow together perfectly here - the author has set a high benchmark for the next book in the series. I'm looking forward to it already.