Rivers of London (2011)

Probationary constable Peter Grant follows a witness statement into a London where rivers have personalities and police work includes learning magic. The appeal is in the joins: interviews, local history, changing neighbourhoods and the practical business of getting across the city. The supernatural grows out of the place Peter already works. Start with this first novel, also published as Midnight Riot, if you like an investigation with a sense of humour and a substantial series ahead.