A group of sixth form students on a weekend retreat at a leisure centre bear witness to a man being set on fire, who subsequently falls from a cliff and drowns in the river below. The victim, Gideon Frane, is discovered to have been a former head boy at a local boarding school for high achieving students, but is also known to have a chequered past, having been responsible for 97 incidents of harassment against his ex-girlfriend. When Billy discovers the cause of death was poisoning, Vera begins to look at the case from a completely different perspective. When the team finally track down Gideon's former best friend, Jamie Levinson, both he and Vera fall victim to a further poisoning. Connections start to build when Joe links the case to the death of a former teacher at their school, whose daughter happened to be present when Gideon was murdered.