Stellan Skarsgård stars as John River, a brilliant police officer whose genius and fault-line is the fragility of his mind. Nicola Walker and Adeel Akhtar line up alongside Skarsgård, as Detective Sergeant Jackie ‘Stevie’ Stevenson, River’s colleague and confidante, and Detective Sergeant Ira King.

As the investigation into Stevie's murder begins to reveal her deepest secrets, River has to question everything he thought he knew about his one true friend. Their relationship might have survived her death but can it survive the truth of who she really was in life?