IT BEGAN with a backstreets killing. Early in May, Jock Davison, a 47-year-old grandfather, was gunned down close to his home in a republican inner-city district of Belfast. The clinically executed murder generated some shock, for such incidents have become a rarity in a city where violence was once commonplace.

Four months on from Davison’s killing, a story of low criminality has become one of high politics, which threatens to derail Northern Ireland’s power-sharing government. On September 10th the region’s first minister, Peter Robinson, stepped aside from his post and pulled most of his Democratic Unionist Party (DUP) out of office. With the Stormont government effectively in limbo, talks are now under way to resolve what has become Northern Ireland’s most serious political crisis in years.

The path from Davison’s murder to political crisis was short. In August, three months after his killing, another local man, Kevin McGuigan, was shot dead in the street by a gunman who is said to have called out: “This is payback for Jock Davison.” Word quickly spread that both men had been figures in the Irish Republican Army (IRA) who had ordered or carried out many murders of their own. Years ago, Davison is said to have ordered IRA members to “kneecap” McGuigan, shooting him in the legs. It seems that McGuigan at last took his revenge in May. Police believe that McGuigan was then killed by associates of Davison.

The two murders raised the critical question of whether the IRA, which was supposed to have decommissioned its weapons and “left the stage” years ago, was back in business. Sinn Fein, the party once regarded as the IRA’s political wing, which now sits in Northern Ireland’s administration, has long insisted that the IRA is defunct. Many suspect that it lives on, but have turned a Nelsonian blind eye so long as it spurns violence.

A detailed picture of the republican underworld emerged when Northern Ireland’s chief constable, George Hamilton, published a description of how the police and the spies of MI5 viewed the McGuigan killing. IRA members were involved, he said, but there was no indication it had been sanctioned by the high command. In an unprecedented statement, he added: “The continuing existence and cohesion of the [IRA] hierarchy has enabled the leadership to move the organisation forward within the peace process.”

This enraged unionists. The small Ulster Unionist Party announced that it would withdraw from the Assembly. Following the arrest on September 9th of Bobby Storey, Sinn Fein’s chairman in Northern Ireland (who was later released without charge), Mr Robinson signalled that the DUP would follow suit. He first called for the Assembly to be either adjourned or suspended, threatening that he would otherwise pull his ministers out of the ruling executive, which could have led to the Assembly’s collapse. When David Cameron turned down his demand for suspension, and other parties blocked an adjournment, Mr Robinson said he would “stand aside” (but not resign) as first minister. Three of his four ministers have resigned; the fourth, Arlene Foster, has stayed on as acting first minister. Mr Robinson will renominate and then withdraw his ministers every week, to prevent nationalists occupying the vacated ministries. The DUP itself admits this is “messy and ugly”.

It has left Northern Ireland with a zombie government. Some committee and other work is still going on, but Stormont’s marble halls and corridors have become much quieter than usual. The Assembly is not technically suspended, but the effect is close enough.

Theresa Villiers, Mr Cameron’s Northern Ireland secretary, has been assigned with finding a fix. She will now spend up to six weeks chairing talks aimed at bridging the gulf between republicans and unionists, with the aim of saving the Assembly from collapse. Relations between the parties have “almost completely broken down”, she said this week.

Prominent on the agenda is the idea of an independent commission to report on the state and behaviour of the IRA, with the aim of reassuring unionists that the organisation has completely disbanded. Of course, this will work only if the IRA does indeed wrap itself up.

With elections to the Assembly due next May, both the main unionist parties have been launching spirited attacks not just on republicans but on each other. That hardly improves the chances of a deal. A recent opinion poll found that whereas a clear majority of nationalists see value in the Assembly, fewer than half of unionist voters regard it as important. Resuscitating the government will require some give and take on all sides; if they feel that little is at stake, unionists may not be inclined to be very flexible.