City of Ruin by Mark Charan Newton
City of Ruin is the second book in Mark Charan Newton's Legends of the Red Sun fantasy series.
Villiren is a city of sin that's being torn apart from the inside. Hybrid creatures shamble through shadows and barely human gangs fight turf wars for control of the streets.
Amidst this chaos, Commander Brynd Lathraea, commander of the Night Guard, must plan the defence of Viliren against a race that has broken through from another realm and already slaughtered hundreds of thousands of the Empire's people.
When a Night Guard soldier goes missing, Brynd needs help. Investigator Jeryd discovers this is not the only disappearance from the streets of Villiren. It seems that a serial killer of the most horrific kind is on the loose, taking hundreds of people from their own homes. A killer that cannot possibly be human. The entire population of Villiren must unite to face an impossible surge of violent and unnatural enemies or the city will fall. But how can you save a city that's already a ruin?