"City of the Lost" by Kelley Armstrong
Casey Duncan is a talented police detective, dedicated to her job and her best friend Diana. Other than her no strings attached relationship with ex-con Kurt, her life is focused on those two things. But Casey carries with her a very dark secret - she once killed a man, and she got away with it. Casey and Diana have been on the run for years, from Diana’s powerful and abusive ex-husband. Once again, he’s found her and now it’s time for Diana to run once more. But when a figure from Casey’s past shows up and threatens her life, the two women realize that they need to go somewhere they will never be found. Diana has heard of a place, a town where people who need to disappear completely can go. Located in the far northern reaches of Canada, this town is their only hope. Casey and Diana are thrilled to be accepted into Rockton, but when they arrive Casey quickly discovers that all is not as it seems. Because a hunter has come to Rockton, and it's hunting for people.