Ben Aaronovitch & Andrew Cartmel 
Rivers of London [PDF ebook] 
Water Weed #2

There’s a disturbing new drug on the streets of London. An unusual and powerful weed, branded with a distinctive logo of a woman’s face covered in tattoos. With strange, vestigia-like side effects for the magically inclined, Detective Peter Grant and DCI Thomas Nightingale are on the case.Using the Thames as a handy link for delivering drugs to buyers might seem like a good idea, but two unfortunate dealers caught the attention of young water goddesses, namely Chelsea and Olympia, who used their powers to steal time for themselves (of course). But in doing so, they’ve provoked the anger of the mastermind behind the cartel. Having already apprehended her two unwitting goons in Bev’s back garden, our heroes are now in the firing line for her escalating campaign of revenge.