The Spotlight team traces how, in the 1960s, suspicion led to unrest between unionists and nationalists, undermining Northern Ireland's government. The arrival of the British Army in August 1969 brought a break in the conflict, and the soldiers were greeted as protectors by many nationalists. That relationship was spoiled by fatal errors and calculated acts of violence. New information about Martin McGuinness's role at that time is brought to light. Ending with the breaking up of the Northern Ireland government, when IRA members believed they were about to force the British Army out of Northern Ireland.

The IRA anticipated that 1972 would be their 'year of victory', only to be countered by a massive British military response in the midst of what became the bloodiest period of the conflict.

When Margaret Thatcher entered Downing Street in 1979, she was confronted by an IRA prepared to conduct a long war of attrition against Britain.

At the end of the Seventies, the IRA built its own internal security system to root out informers. But British intelligence found a fatal flaw that unlocked many of the IRA's secrets.

Traces how unionist anger grew as IRA attacks on the security forces killed members of their community. When Margaret Thatcher signed the Anglo-Irish Agreement in 1985, giving the Republic of Ireland political influence in the North, the anger spilled over into talk of insurrection. The programme reveals how loyalist groups rearmed and used intelligence leaks from soldiers and police to boost their campaign of killing, including new information about MI5 agents operating inside the largest loyalist group, the Ulster Defence Association.

Loyalists killed more people than the IRA in the closing years of the Troubles. Through an insider in one of the most notorious killer gangs, Mandy McAuley discovers that not only was the Ulster Volunteer Force carrying out more attacks, it was also deliberately targeting families of Irish republicans. Revelations about the murders of two young brothers lead to calls for the investigation into the killings to be reopened.

How the UK government policy changed, from seeking to destroy the IRA to bringing it to peace. And how secret talks, doublespeak and smart tactical maneuvering ensured that Gerry Adams was able to persuade the IRA to go with the deal. In this final episode of the series, reporter Darragh MacIntyre hears the inside story of the peace process from within the IRA and the British government. He discovers new information about the internal battle for control of the IRA during the most delicate days of the peace process and learns about the scale of secrecy that still surrounds the conflict.