Darkness Hunts is the fourth book of the Dark Angel series about Risa Jones, half-werewolf and half-Aedh woman who was in an unfortunate circumstance that involved with her existence as the daughter of an Aedh who had created several keys that could unlock and lock the doors between the realms where everyone wanted her for the power to wield the keys. All include the vampire council, the Raziqs, other kind of monsters and also the heavens where a reaper Azriel were sent down to shadow Risa wherever she goes. However, bad things tailed her wherever she goes, starting from her father trying to launch her into finding the missing keys and the unexplained slaughter of her mother, the attraction between a fallen Aedh, Lucian that spiraled her down into a mess when Lucian himself isn't what he seems, to the Raziqs tortures and her friends problems that seemed to have come from the mess she was in. Risa was in an ultimate limbo where she was in the middle of everything where her world had turned a full 180 degrees around her. 
 In this book, we are focused on the previous books about the ley lines and Risa's inability to communicate with the dead. When she astral projected herself to talk to someone who had died in the previous book, she heard a scream and when she decided to investigate it, she found herself with an unknown adversary who taunted her to save the woman's life. When Risa tried to save the woman, she was too late. The killer then found ways to taunt Risa via the directorate where he had already developed a reputation as a serial killer and offered Risa another chance to save the life of his future victims. If she was fast enough that is... 
 I had my suspicion on Lucian and this mirrors with Azriel's frustration with Risa's relationship with the Aedh and their new problem of assimilating with each other that made the reaper and Risa's attraction becoming more forbidden. But Risa began to notice that Lucian might have done something to her that made him irresistible to her and I was glad that this book pan out with that line of the story. He had become one of my suspect in the book and he does get even more suspicious than ever. 
 As for the mystery plot, I do enjoy the cat and mouse chase between Risa and the unknown serial killer. But the overall plot about the keys became stunted since Risa's became embedded by the device that warned her father's presence to the Razan. 
 I did enjoy the mystery more than the story about the whole key mess and since the book have three more in the series, it does hooked me as a crime story than as a paranormal book so I will wait for the subsequent installments of the series to satisfy my curiousity.