Simon Spurrier 
Damn Them All #2 [PDF ebook] 

Dora, a detective traumatized by the same recent supernatural events as Ellie, is suspicious of the untimely death of Alfie-a man who helped her in desperate times. As new terrors unfold, the two witness strange changes to the political landscape of Britain: a gibbering madness infecting the population. Ellie fears the worst, and seeks the only thing she thinks can help. A demon may be behind what’s happened, one that predates even the Ars Goetia and isn’t so easy to control