Episode One: originally transmitted on ITV, 3 June 1990

Northern Ireland, 1982 to 1984.

County Armagh. Explosives are taken to a hayshed off Ballyneery Road North, tracked by RUC Special Branch, who were forewarned by an informant. The RUC place the hayshed under surveillance, including an MI5 listening device. A dumper truck battery is reported stolen on the Kinnego Embankment. Granted special dispensation from Special Branch who restrict Kinnego visits, three RUC officers investigate but are killed by an IRA landmine. Despite surveillance, the hayshed explosives were used at Kinnego. Special Branch presses their informant for the bombers' names. He is paid.

A special support unit trains to eliminate terrorists using firepower, speed and aggression: in training, Constable Robinson wrongly shoots a dummy hostage. The informant claimed that Eugene Toman, Sean Burns and Martin McCauley were responsible for Kinnego and now plan to assassinate an RUC reservist. George Flanagan addresses a Special Branch briefing to stop them.

A long surveillance ends in confusion rather than the planned vehicle control point. The special support unit chases a car and opens fire. Its three unarmed occupants are killed: Toman, Burns and - instead of the expected McCauley - Gervaise McKerr. Flanagan obstructs CID investigations. Protecting their informant, senior figures including RUC Chief Constable Sir John Hermon discuss a line, which becomes the media's report: a car failed to stop at a routine checkpoint, injuring an RUC officer. Flanagan's debriefing suggests officers thought they saw gunshots and returned, not opened, fire. Constable Brannigan repeats this story to CID, and denies firing after the car stopped.

The informant leaves a message about the hayshed. At the hayshed, the informant talks to Michael Tighe, who feeds the farm animals for their absent owner. Observed by Special Branch, McCauley and Tighe ride a motorbike. McCauley finds three old rifles in the hayshed and calls to Tighe. Hearing McCauley, Flanagan orders the hayshed to be cleared. The special support unit arrives, shooting without warning, killing Tighe and injuring McCauley. There is no ammunition, nor any explosives. The MI5 device has recorded everything. Reported on TV, the RUC claim a routine patrol followed a gunman to the barn, had guns pointed at them, shouted warnings then opened fire. The officers privately call this fiction. There are reports of Tighe's innocence and requests for an enquiry. McCauley is charged with firearms possession and conspiracy to murder.

Targeting Dominic McGlinchey, head of the INLA, Special Branch follow Roddy Carl and Seamus Grew on their journey, encouraged by an informant, to rendezvous with McGlinchey in the South, but cannot capture McGlinchey until he enters the North. Handling surveillance, the Army loses Grew and Carroll. Robinson's car collides with an Army vehicle before a control point can be established. The suspect car passes. In an unmarked car, Robinson and colleagues chase, shooting. Robinson opens the door and shoots the driver. Unarmed, Grew and Carroll are killed, but McGlinchey is not in the car.

Flanagan proposes a cover story: Robinson, called after a car crashed the control point and injured an officer, gave warnings and fired from his car in self-defence. Verifying detail is concocted: an officer lies on the ground for forensics, the armourer changes the time weapons were issued, and the transport officer is told to dispose of Robinson's crashed car without an accident report. CID say forensics prove he opened the door to shoot Grew. Robinson says he was ordered to lie. In his murder trial, Robinson lists things senior officers ordered him to hide from CID, including the use of an informant, to disguise a planned encounter as a chance encounter.

The Stalker Inquiry is convened. Hermon disapproves but is reassured it will report to him. The Regional Inspector of Constabulary warns that Hermon may be unhelpful but reassures Stalker that his findings will be acted upon. Stalker records this conversation.

Stalker's team arrives in Belfast. Stalker and his number two, Detective Chief Superintendent John Thorburn, meet Hermon. Stalker wants to re-examine the three shootings and recommend prosecutions if necessary. Hermon claims he, not Stalker, decides what goes to the Director of Public Prosecutions. For Hermon, it is the IRA, not the RUC, who have a shoot-to-kill policy. Stalker's team enters its offices in a former hotel. Their offices are bugged.