Ben Aaronovitch & Andrew Cartmel 
Rivers of London: Black Mould 
Black Mould #4

Peter Grant: policeman, trainee wizard and now pest controller. Joined by fellow officer and Muslim ninja, Sahra Guleed, the two are trying to contain an outbreak of vindictive black mould that seems to be going after the rich and heartless.But after a successful mission, the mould has penetrated the headquarters of London’s crime-fighting magical practitioners – The Folly – and the shiitake is really about to get real…