The End of Darkness — Jaime Rush

His noble heart brings her to life … his Darkness could kill her. Erica Evrard lives for one thing: using a mysterious power she calls Lightning to hunt down and destroy serial killers. She knows her ability will someday claim her life, but it's a price she's willing to pay. Now after the Heart Ripper, she discovers that her quarry possesses a dark, paranormal energy. When she meets Magnus, the sexy drummer at a local bar, their first encounter is both passionate and disastrous. Even worse, she suspects that he may hold the same energy. Magnus McLeod indeed harbors Darkness, having been infected while saving a woman. He is learning to harness it -- and keep it from overtaking him. He'll need to learn fast, as he and Erica are captured by supernatural humans whose plan threatens an entire Arizona town.