Graham Young, played by Hugh O'Conor, has been fixated on death and the macabre since childhood. A brilliant chemist with a sharp mind, he secretly dreams of poisoning as many people as he can and studies ways to do it. In adolescence, he poisons a schoolmate to win the attention of a girl who was seeing him, leaving the other boy ill rather than dead, while Graham’s conversations with his date spill vivid, graphic imagery of deadly car accidents. He also devours a graphic comic-book account of a wartime act in which the Dutch Resistance killed a German army camp by poisoning their water supply with thallium, feeding his already chilling fantasies.
At the age of fourteen, Graham is arrested outside his home in Neasden after poisoning his father and his stepmother with thallium, killing the latter and leaving his father gravely ill. During the struggle with the police, he drops his “Exit Dose,” a backup plan he intended to use to take his own life if caught. He is hospitalised for nine years in an institution for the criminally insane, where a dedicated psychiatrist works with him in the hope of rehabilitation. The doctor quickly notices Graham’s pattern of deceit, as the young man appears to offer little of himself and even borrows dreams from a fellow prisoner. That exchange dissolves when the fellow inmate commits suicide, and the source of the deception is laid bare. Yet the doctor persists, and over time he manages to secure Graham’s release despite the early signs of manipulation.
Back in ordinary life, Graham takes a job at a camera factory, where he is shown the secret ingredient used in the company’s shutter system—thallium. It isn’t long before he resumes poisoning, killing two coworkers by lacing their tea with tainted thallium stolen from the laboratory, and sickening many others. For months, the exact source of the illness puzzles the workers and management alike, until a twist of hygiene procedures reveals the culprit: all personalized teacups are replaced with uniform ones to reduce the risk of targeted poisoning. Graham’s careful memory work to match each cup to its owner becomes a telltale clue, and his colleagues finally realize what has been happening. The authorities soon arrest him, and he is sentenced to a lengthy period in an ordinary prison.
During his life in custody, Graham’s past is revisited, and the path that led him there is laid bare. The story culminates in his suicide, a fatal end brought about by poisoning himself with the so‑called Newton’s Diamond he had crafted during his time in the psychiatric hospital. Throughout, the narrative probes the uneasy boundary between extraordinary intellect and dangerous compulsion, presenting a chilling portrait of a young man who channels a morbid curiosity into real, deadly harm.
Ray, a supervisor at the factory, Arthur Cox, features in the factory sequence as the new hygiene measures unfold and the investigation tightens, underscoring how ordinary settings can become the stage for extraordinary peril. Dr. Ernest Zeigler, the psychiatrist who engages with Graham during his earlier confinement, is portrayed by Antony Sher, and his professional vigilance shapes the arc of Graham’s early examination and eventual release.
