A mysterious death at a spiritual retreat pulls Jasper into the orbit of the enigmatic Lady Cynthia, and the post-mortem shatters the guests' identical stories of an open and shut case. As tensions spike and a near-confession is abruptly cut short, Jasper's unresolved grief for Adelaide shadows his every move, heightening the pressure on both the case and his fragile bond with Helena.

As Jasper turns to tech to manage his spiralling OCD, the murder of a golf instructor and a taunting cipher ignite fears of a serial killer. A rare error from the Professor heightens tensions as the ciphers grow bolder. Meanwhile, Leonie's bond with her father, Chester, is pushed to breaking point by his deep-seated hatred of the police as Dan is caught between loyalty and duty.