I don't normally read urban fantasy, but this combination of a police procedural and a little light-hearted magic was irresistible. It's funny, the protagonist is very likeable and it's a very pleasant way to spend some Christmas money. But I do find urban fantasy unsettling, and I'm not sure why. I can be quite happy reading about a wizard meeting a balrog in the Mines of Moria in company with two men, four hobbits, an elf and a dwarf, but a wizard meandering round Covent Garden and Hampstead and Staines chasing after a malevolent ghost in company with a river sprite seems kind of weird to me.
The problem with all urban fantasy is that, without the usual world-building going on in the background, it throws the other aspects - plot, character, magic - into sharper relief. The characters here are all perfectly nice and believable, but they're mostly terribly ordinary, especially the hero, Peter Grant, and his colleague and would-be girlfriend, Lesley. The 'wizard' is rather ordinary, too - a little eccentrically dressed, perhaps, but in London that is unremarkable. Only the river spirits have a bit of character, but there too they are superficially ordinary folks who just happen to be river spirits, and the joke wears a bit thin after a while. The magic is a bit Harry Potter-ish, only without the magic wand, in that a Latin word is associated with each 'spell', so nothing very unusual there, and the plot is fairly slight, too. So not many big surprises, and I found it a bit dull in places.
If this sounds a bit negative, it's mostly because I'm used to reviewing books where these things matter. Here, they don't, much, because it's simply a charming and amusing way to pass the time. The hero is a nicely laid-back sort of guy, the humour is premium quality dry British and the murder-mystery style is more Agatha Christie than anything else (or maybe Midsomer Murders - cosy with a slightly surreal twist). It's not earth-shattering (but then it doesn't try to be), it's just plain good fun and I liked it. And Peter must be the nicest protagonist in the world. I wanted to give it four stars, if only for the humour, but realistically it's a three.