June 1967. A missing persons case of a Dutch au pair proves far from routine, pulling Endeavour into the duelling worlds of Oxford scientific academia, the city’s vast parks, Night School and the untamed wilderness of the Oxfordshire countryside. Connected to the investigation is an august family of three troubled siblings. When a suspected link between the au pair’s disappearance and a cold case from years back is unearthed, unconventional methods in that investigation created fraying tensions across the police force. As the body count rises, Endeavour deduces that there may be darker forces at play.