An aging detective, now retired, is living in a remote Sussex farmhouse with his housekeeper and her young son. Struggling with the early stages of dementia, he reflects on his past cases and wrestles with the limitations brought on by his fading memory. His current obsession is a 30-year-old unsolved case that led to his retirement: the mystery of a troubled woman. Haunted by his inability to close it, he attempts to reconstruct the details by reviewing his notes and recalling fragments of his memories.

Simultaneously, he forms a bond with the housekeeper's insightful and curious son, who shares an interest in sleuthing. As they delve into the past together, he gradually uncovers missed cues and dangers, which helps him come to terms with his own humanity and vulnerability. This journey of rediscovery provides profound insights about guilt, memory, and the importance of compassion, leading him to a poignant revelation about the nature of his identity and legacy.