The Vast Abyss

The finale opens at the scene of the fourth attack and learns that this victim is still alive. Gibson sees the discarded ligatures and the method and knows the same man is responsible. Annie Brawley is taken to hospital in a coma, and the investigation puts its weight into the trace evidence on her body and the chance she will identify her attacker, the first living witness the killer has left.

Gibson and Sarah Kay's father, Ian Kay, make a televised appeal, and Gibson adds an unusual offer: if the killer comes forward, he will be able to speak to her personally. A photofit of Peter, built from Rose Stagg's account, is published, and the appeals produce the break. CCTV of Sarah Kay's last movements that evening shows Spector following her through the gates of the municipal gardens. Sally Ann Spector, now pregnant, sees the footage, recognises her husband behind Sarah Kay, and tells him he has to go to the police station to eliminate himself.

Spector goes to the PSNI and gives a statement, fingerprints and a DNA sample. Sally Ann supports his false account that he was at home on the night of the attack on Annie Brawley, which puts her in the position of having given a murderer a deliberate alibi. When she confronts him about his nights away, he tells her a lie that will damage his family more than the truth might have: that he has been having an affair for three months with the children's babysitter, Katie Benedetto, who is fifteen. Sally Ann leaves him briefly and is won back, still believing the affair and not the killings.

The corruption strand is finished without being resolved. DCI Eastwood accuses Burns of weakness for passing information to the Monroe family and so allowing Aaron Monroe to escape, and Gibson's own night with Olson remains inside the inquiry. No source consulted names the gunman who killed Olson. The episode's centre is the telephone call. Spector, having given his statement and decided to leave Belfast, rings Operation Musicman and is put through to Gibson, the first time the two speak. He tells her he is going to stop, that he is going away, and that she has lost. She answers that what he does is not philosophy but misogyny, the age-old violence of men against women, and tells him she knows more about him than he thinks. When the call ends he leaves Ireland with Sally Ann and the children, to settle in Scotland.

The final scene is not Spector's but Annie Brawley's. The comatose victim wakes, and the series' last beat leaves the survivor able to name her attacker and the killer out of the police's reach, the credits running over an unresolved case.

The strength is the telephone call, the only scene in the first series in which the two leads speak, and it makes Gibson's argument about misogyny land as an answer to the killer rather than as a speech to colleagues. The weakness is the unresolved ending, and the sources disagree about whether withholding it is a fault or a strength. The Guardian called the cliffhanger an exquisite torture and found that Spector's motive, a reference to a childhood in care aside, remained unclear, and that the corruption subplot was left a mass of political and police detail. Cult-fix complained that nothing was answered; the openDemocracy essay defended the absence of resolution.

It is the point at which the series chose serial continuity over a closed story, the decision that shaped the whole programme and the reason it is discussed as one continuous story rather than three separate cases. It also ends the series' single-director run: Jakob Verbruggen did not return for series 2 and Cubitt took over directing. Its audience of 4.65 million on BBC Two was the highest of the first series in the BARB table, though a later Guardian report put the finale nearer four million.