At the weekend, a senior security source spoke of the state of play within the Ulster Defence Association, one of Northern Ireland's two largest Protestant paramilitary groups.
UDA gunmen from west Belfast had killed Eddie Treanor, the Catholic man killed in a shooting attack in north Belfast on New Year's Eve, he said. The attack was claimed by the smaller Loyalist Volunteer Force but, he added, "really, the only thing the LVF supplied was the codeword for the claim".
Since then the UDA leadership had met and decided to hold itself in readiness. If Protestants were killed by republicans the UDA leaders would meet again to decide what to do. But if anyone with UDA connections was shot, no meeting would be necessary: units could go ahead with immediate retaliation.
Yesterday somebody with UDA connections was shot. Jim Guiney, killed in his carpet shop in south Belfast by the Irish National Liberation Army, was a leading loyalist associated with the Ulster Democratic Party, the UDA's political wing.
And so last night a Catholic taxi firm employee was shot and killed in south Belfast. It does not need access to intelligence assessments to theorise that it was almost certainly a UDA inspired revenge attack.
Bill Stewart, a senior RUC commander in Belfast, said: "This is another senseless and indiscriminate act which can achieve nothing, only further suffering. I appeal to all people of influence to do all in their power to prevent further bloodshed."
The cycle of tit-for-tat is a long-established feature of Belfast's macho paramilitary underworld. The INLA has struck: it is now the UDA's turn to strike back. Many of Belfast's deadly acronyms are now back in action.
The INLA has long been the joker in the republican pack. Always a separate organisation from the mainstream republican movement, the IRA and Sinn Fein once regarded them as brothers in arms. Three of the 10 hunger-strikers who starved themselves to death in 1981 were INLA members.
In recent years, however, it has tended to be derided by the IRA as small-scale, apolitical and disorganised. It also has an extraordinary tendency to turn in on itself in periodic outbreaks of feuding. These bouts are so savage that INLA members have probably killed more colleagues than they have murdered members of the security forces.
During 1996, for example, the six people it killed were made up of five men associated with it together with a nine-year-old girl killed during a feud attack. In 1997 it had only two victims, the first of whom was an off-duty RUC officer killed in a Belfast gay bar. But the second victim, was Billy Wright, the LVF figure killed in the Maze prison just after Christmas.
His death sparked off the present cycle of political tension and violence, with three Catholics killed in retaliation by the LVF and one by the UDA. Although the fact that Eddie Treanor was a victim of the UDA is common knowledge, most in the political world have turned a Nelsonian blind eye.
This is because the UDP, the UDA's political wing, is one of the eight parties in the Stormont multi-party talks. Although it is one of the smaller parties there, it has added significance in that its moderate political approach is very much to the liking of both London and Dublin.
Similarly, security sources are convinced that the recent attempted murder of a man in a bar in south Belfast was the work of the IRA, acting under the fig-leaf of yet another acronym, DAAD (Direct Action Against Drugs.)
Strictly speaking, anyone at the Stormont talks table connected to organisations still active in violence is supposed to face expulsion. But everyone knows that ejecting the UDP would seriously damage the talks process, as well as probably sending the UDA back into all-out violence.
This helps explain why few inquired too deeply when the UDA was last year seen to be responsible for two deaths - that of a Catholic civilian and one of its own members killed in a mysterious "own goal" explosion. This became known as the "no claim, no blame" syndrome: the UDA did not admit involvement, and most politicians glossed over the question of responsibility
The prospect is, however, that the UDA might now attempt to take its revenge on a scale which simply could not be ignored. A number of shots were fired in the attack which killed Eddie Treanor, but only one of them came from a machine-gun. The fact that the weapon apparently jammed may have saved many lives that night.
But the grim possibility is that this time the UDA will be intent on exacting its revenge on a larger scale. If it succeeds, Ulster will face both security and political crises which could test the peace process to its limit.