DCI Adam Dalgliesh is sent to a nursing school to investigate the death of Heather Pearce, a student poisoned during a demonstration. But as he uncovers the secrets that infect the school, can Dalgliesh identify the killer before they strike again? Guest stars include Fenella Woolgar (Call The Midwife), Richard Dillane (Young Wallander) and Amanda Root (Baby Reindeer).