Dr Harold Shipman successfully holds a charity auction for his patient fund. On 29 May 1997, Shipman signs a death certificate, then injects his patient, Ivy. He sees other patients while Ivy lies dead behind screens. Six months later, funeral director Debbie Bambroffe tells her father, Alan Massey, her concerns over Shipman's diagnoses of heart trouble in sudden death cases.

Debra King has reduced the drug dosage prescribed by Shipman for her husband Jim's terminal cancer. Debra refuses to let Shipman administer more drugs for what she rightly suspects is pneumonia. A hospital doctor realises that Jim has been prescribed fifty times the normal daily dosage. Shipman responds sympathetically to Alan's concerns over his high cremation rate and shows his death certificate register. Alan believes Shipman's reputation as a conscientious doctor.

December. Jim's father prepares for a flu jab from Shipman, despite reservations about Jim's treatment. Shipman asks Debbie for three cremation forms. Jim learns that his father has died. Debra is surprised by Shipman's failure to insist on an autopsy.

At another surgery, Dr Linda Reynolds discusses her concerns over Shipman's practice, particularly the number of deaths involving people with no prior potentially fatal illnesses and, in particular, a high cremation rate. Reynolds alerts the Medical Defence Union, which informs a coroner.

Shipman informs Jim that he does not have terminal cancer, but that the hospital made an incorrect diagnosis. Investigating Reynold's claims, Inspector Dave Smith finds no evidence against Shipman in his cremation records.

Shipman asks Kathleen Grundy to participate in a study into ageing which he's conducting for Manchester University. She signs a consent form in front of witnesses. Shipman types a will. He injects Kathleen at her home. He enters information on his computer. Grundy dies that day and Grundy's daughter and solicitor, Mrs Woodruff, queries Shipman's verdict of old age, but Shipman suggests sparing the family an upsetting post-mortem. When told that Grundy sent a new will to another solicitor by post, Mrs Woodruff investigates and discovers that it was forged, with witness information taken from the witnesses to the consent form. Investigating, Egerton has Mrs Grundy exhumed and the police search Shipman's practice.

The investigation prompts some locals to verbally abuse Egerton for hounding Shipman, but others report long-held suspicions: John Shaw's list goes back to 1992. Shaw apologises for not acting sooner, but Egerton may not have believed him even one month ago. Toxicological tests on Grundy reveal massive quantities of morphine. Shipman was convicted in 1976 for abuse of controlled substances and forging prescriptions; Egerton wonders about the General Medical Council's decision to allow Shipman to set up on his own.

During police questioning, Shipman claims to have left Grundy alive after taking a blood sample, but this sample never arrived at its purported destination. He claims that Grundy regularly borrowed his typewriter, but is accused of forging Grundy's will. He was not working with Manchester University, and denies saying that he was. Shipman explains the fatal drug intake by opening medical notes which reveal long-term doubts about Grundy possibly using drugs. Shipman is asked why he did not therefore order a post-mortem. Examination of Shipman's computer reveals that his records on Grundy were added after her death. Shipman is charged with murder.

The police discover that Shipman had been stockpiling drugs by prescribing to dead cancer patients: although banned from having addictive substances, he was allowed to prescribe them. The police think this system is ripe for abuse.

Shipman's fingerprint is found on Grundy's will. Egerton and Reverend Thomas debate whether Shipman was born evil or motivated by playing God; Egerton dismisses the idea that it was triggered when, as a teenager, he saw his dying mother administered with drugs. More of Shipman's former patients are exhumed.

While denying Winifred Mellor's murder, Shipman is shown evidence of his computer falsification. He cannot answer. Later, Shipman suffers a possible nervous breakdown. Egerton is angry that Shipman is upset only for himself.

On 31 Jan 2000, Shipman is convicted of 15 murders and sentenced to 15 life sentences. The CPS may make further charges. Egerton lights candles for the victims, but doubts that the story is over.