Night Rounds by Helene Tursten

When the power goes out at Lowander Hospital, the staff is concerned with saving a patient's life. The patient dies and Nurse Siv then sees the roaming ghost of Nurse Tekla, who died sixty years ago. The body of another nurse, Marianne, is found in the hospital's electrical room, leading Siv to believe that the murderer was Tekla. DI Irene Huss is called to the hospital, with her colleague Superintendent Sven Andersson, to try and make sense of what happened. When another nurse and a homeless woman who possibly saw the killer also disappear, Irene realizes the past might hold clues to the present. Night Rounds is the second book in the Irene Huss series, but the fourth to be published in the U.S. It's been five years since the last book was published, far too long for readers who enjoy spending time with Irene--a fortysomething mother of teenage twins who's married to a chef.