Deputy Assistant Commissioner Charlie Hillian is brutally murdered on the night of his retirement party, sending shockwaves through the Oxford police force. Hillian, a former senior officer and Morse's one-time boss, had been working on a book detailing his most memorable cases, including an unsolved 18-year-old mystery involving the death of an 8-year-old girl. The manuscript's chapter on that case goes missing the night of his death, raising suspicions about a possible connection to his murder. 　　The investigation quickly narrows in on several key suspects. Frederick Redpath, the prime suspect in the girl's death years earlier, was seen at Hillian's house on the day of the murder. Hillian's ghostwriter, who stands to inherit all book royalties, also comes under scrutiny, as does a handyman working on the property. Meanwhile, Redpath's daughter, who had a personal connection to the deceased girl, adds another layer of complexity to the case. 　　As Morse delves deeper, tensions rise with DCI Dawson, a protégé of Hillian, as they reopen the cold case of the girl's death. Their conflicting approaches and personal loyalties create friction, complicating the investigation. Morse must navigate these professional rivalries while piecing together the truth behind Hillian's murder and the unresolved tragedy from years past.