The murk looks set to increase, and it was a murky year. It ends with the Taoiseach saying once more that he wants to see Ian Paisley's Democratic Unionists and Sinn Féin sharing power in a restored devolved government - because that's the agenda of the Good Friday agreement for "the betterment" of Northern Ireland, writes Fionnuala O Connor
But the Taoiseach also insists that any partnership between a Dublin party and Sinn Féin would mean disaster for the Republic. His party colleague John O'Donoghue has just repeated the mantra that Mr Ahern and Minister for Justice Michael McDowell have been chanting for most of the past 12 months, that Sinn Féin can not be in government in the Republic.
Though even Mr McDowell said recently that there was no evidence of continuing IRA criminality, Mr O'Donoghue boosts his argument by claiming that the IRA is "still there". Ministers simultaneously denounce SF as a ruthless conspiracy to overthrow the State, while urging SF to assume responsibility for policing and justice, and government, in the North - an outcome which would assuredly boost their electoral support in the South.
And the awkward fact meanwhile sits there, elephantine in the Dáil sitting-room: that there are more Sinn Féin voters in the South now than the North.
Elections are closer in the Republic than Northern Ireland. The political establishment's evident panic is likely to increase. Perhaps it is the frustration of having to talk up those conspirators in the Northern arena, while decrying them in the South, that produces the occasional ministerial combustion.
To add to the moment's sour-sweetness, Sinn Féin faces into 2006 in a state of shock. The Denis Donaldson affair will hurt for a long time. The republican machine is making the best of it and churns away at the old "what else would you expect from the Brits" line. But the aftershock is colossal, no matter how disguised.
The Sinn Féin vote North and South will at least hold up and more likely increase in the next elections: the Donaldson business may not even register in the South. But it will go on troubling Northerners for years. How could it not, when solid ground has become impossible to distinguish from swamp? The surest bets are that republicans did indeed conduct a widespread spy ring at Stormont, and that more secret agents will emerge. Was Stormontgate designed to help David Trimble and bring down power-sharing? Some will cling to that as a satisfying piece of dirty trickery, but there may never be proof one way or the other.
A spy whose betrayed colleagues flank him one day to declare his virtue and days later expel him for treachery unsuspected over 20 years: no thriller-writer who wanted to convince would touch that sequence, not to mention the Northern Bank robbery. What fiction would make events stuffed with such improbability bookend a single year? If Sinn Féin's leaders were even a bit less ruthless, it might be possible to feel a little sorry for them. Only the discipline of plotting murder for decades and regarding the outside world as the enemy has kept a great howl of internal anguish out of unfriendly earshot.
"My name is Denis Donaldson . . . " The video clip of that bald little statement will recur in every end-of-year review, every future documentary on modern republicanism.
Dissident republicans lavish scorn on the Sinn Féin leadership in letters-columns and phone-ins, building up a picture of a joint British-SF peace strategy put in place with the help of who knows how many agents. At street and even at middle-ranking level, fury at Donaldson is still fighting it out with shock, bafflement at how long he was able to deceive so many, and an emotion very like bereavement.
Many "ordinary republicans" shrugged off the murder of Robert McCartney - in spite of his eloquent sisters - and were blithe about the Northern Bank.
Donaldson's confession was different. Suddenly the untouchable authority of Gerry Adams and Martin McGuinness, frontmen long-schooled against spontaneity, looked scratched. Grim faces behind Donaldson one day became worn, anxious masks a week later.
Apparatchiks much like Donaldson in age, length of service and prison experience, trotted out slightly pathetically to claim that Denis in fact had little importance: belonged to the outer not the inner circle, never ranked high in either IRA or Sinn Féin.
The cast had little rehearsal, and some lines were out of place. "If there ever was a stereotypical mould for an informer then Denis Donaldson broke the mould," was how his old friend Jim Gibney, a veteran press handler and fellow Short Strand native, put it in the Irish News. Informers were an occupational hazard who had put Gibney in jail three times, he wrote, so he should not be surprised, "but I am, that Denis crossed to the other side". The ripples are still spreading.
Sinn Féiners have Southern politics rattled, but they will be glad to see the back of 2005.