Rivers of London is, more or less, an urban fantasy starring DC Peter Grant of the Metropolitan Police, who is transferred to the magical branch of the Met (consisting of hundred-year-old wizard Nightingale and his possibly-a-vampire servant Molly) as a result of a meeting with a Cockney ghost. Before long, a spate of horrible magical crimes are being committed across the city, and Nightingale and Peter must find a way to stop them. And, just to add a bit of extra excitement, Mother and Father Thames are in the throes of an ancient feud that also needs sorting out pronto.
Aaranovitch has a deliciously funny narrative voice that reminds me somewhat of Neil Gaiman's Neverwhere; perhaps my favourite passage in the novel goes like this:
""So magic is real," I said. "Which makes you a...what?"
"Like Harry Potter?"
Nightingale sighed. "No," he said, "not like Harry Potter."
"In what way?"
"I'm not a fictional character," said Nightingale."
But I did feel that that same cynical humour sat uneasily with Grant's unquestioning acceptance of the world of magic - his behaviour didn't quite match up with his sardonic narrative voice. There are also moments when he launches into long passages of information with no indication of how he came by that information - it isn't exactly textbook policing.
On the whole, though, it's well-plotted with a fascinating premise and a nicely magical denouement, although the mystery never seems fully resolved - we know who, but not why, or how. Still, I can see myself reading the sequels one day.