Sanday, one of Britain's northernmost islands, is remote and often inaccessible. When human remains are discovered behind an old primary school, forensic expert Doctor Rhona MacLeod arrives to excavate the grave. Approaching midwinter, daylight is scarce, the weather inhospitable and the residents uncooperative. When the death of an old man in Glasgow appears to have links with the island, DS Michael McNab is dispatched to investigate. Then a series of unexplained incidents occurs, apparently linked to the discovery of 13 magic flowers representing the souls of dead children who had attended the school. But how did they die? And why are their deaths significant?