Dr Nina Crawford of the University of Glasgow's Veterinary College - driven, fanatically dedicated, a survivor - is one of the most respected equine surgeons in the country. But now she seems to be losing her grip, on her operating theatre, on her skills - and on her mind. A surgeon's worst nightmare is coming true before her eyes: "The operation was a great success, but the patient died." All of her cases are dying after routine surgery and she has no idea why, or how, or what to do to stop it. Under the fierce scrutiny of those around her, Nina feels herself spiralling into the depths that led her, years before, to attempt suicide. Kellen Stewart is Nina's therapist - and also her friend. Now her own horse needs emergency surgery and Nina is the only one who can do it. As the boundaries blur between friendship and professional relationship, it becomes clear that it's not only the horses' lives that are on the line.