There were two subtly different plays on the jigsaw metaphor last night, as the Taoiseach and the British Prime Minister met for dinner at Downing Street to review progress in the peace process negotiations.
All the pieces were on the table to create a comprehensive political deal, according to the new Northern Secretary, Dr John Reid. The question was how to fit them together.
But as a Dublin source saw it, there were three pieces left to put in place. "We know how to fit them. The question is persuading the main players to fit them."
The three elements to an agreement are policing, demilitarisation and putting paramilitary arms beyond use. Policing is causing most difficulty.
The British government is trying to reshape the police reform package more to the liking of the SDLP and Sinn Fein without amending the legislation. There's a balance to be struck. If he doesn't call it right, Mr Tony Blair could win Sinn Fein but lose the Ulster Unionists. Any new deal must be sufficient to allow David Trimble, at election time, convincingly argue to his constituency that "the Belfast Agreement is Good For You".
On Tuesday night, one got a sharp impression of why the SDLP and Sinn Fein are laying such emphasis on their demand for retrospective powers of inquiry into past actions of the RUC and British army.
UTV's Insight programme publicised a damning report by the human rights group, British-Irish Rights Watch, accusing the British army of being a party to institutionalised murder. The report also implicated the RUC Special Branch.
It is hardly surprising that the SDLP and Sinn Fein want to ensure they can at least say such matters will be properly and independently investigated. Mr Ahern and Mr Blair, as well as British and Irish officials, have been engaging in hard-talking behind-the-scenes contact over recent days with the main players in Sinn Fein and the SDLP. The SDLP, at least, appears reasonably confident its concerns will be met on policing.
After phone calls with the British and Irish leaders, Mr Gerry Adams would only say there was still a "wide gap" between what republicans want and what the British government is offering. Among his main demands are more scrutinising or accountability powers for the policing boards, as well as guarantees the emblems of the new force will be neutral.
He was hanging tough yesterday, but said if Mr Blair put forward new proposals that did not involve revisiting the legislation, he would carefully study them.
The time for negotiation is drawing to a close. Mr Ahern and Mr Blair were last night putting the final touches to a framework they believe deals with the three interlocking issues. The deal will involve risk-taking by the SDLP, Sinn Fein and Ulster Unionists, but the judgment call of the Taoiseach and Prime Minister is that decision time has arrived.
The mood last night was still positive, although the two governments and the parties were entering the usual caveats. Mr Ahern and Mr Blair are prepared to clear their diaries and return to Hillsborough by the weekend, or next week.
At Hillsborough there could be some final horse-trading to be done. But not much. What last night was about was the British and Irish leaders' agreeing that now is the time to put the jigsaw together.