It happened at lunchtime on Wednesday, as three of the four lead players in the drama of this week, all exhausted from their late-night negotiations, gathered for the fourth time.
Martti Ahtisaari, the doughty Finnish President, Strobe Talbott, US Deputy Secretary of State, and Viktor Chernomyrdin, Moscow's special envoy, had already met twice, in Helsinki and the previous week in the former Moscow dacha of Joseph Stalin.
The Moscow meeting, by all accounts, helped to lay the basis for a potential deal. It drove home to Mr Chernomyrdin that the US would never back down on the conditions set by Nato for a ceasefire. At the same time the American and EU envoys conceded for the first time that Russian troops would play a major role, and that a small number of Serb troops could remain in Kosovo to defend religious sites.
But the Petersberg meeting was the crunch one: called against the advice of Mr Ahtisaari, who believed Moscow was not ready to compromise. At 2pm he was proved wrong as Mr Chernomyrdin finally signed up to a formula incorporating Nato's five demands.
When Mr Ahtisaari's Finnair jet touched down in Belgrade later that afternoon, there was still every chance the deal would go awry. Conscious of Slobodan Milosevic's record, the veteran Finnish peacemaker decided not to conduct any form of debate with him. Face-to-face he delivered the message to President Milosevic in slow, deliberate tones. This was not a negotiation, he said. "This is the best deal you are going to get."
During the four-and-a-half-hour meeting, Mr Milosevic sat unsmiling, but the tone remained, according to Mr Ahtisaari, "very businesslike", with "no voices raised in the discussions. We went through the paper. I tried to clarify the issues that were raised." It was also made clear to the Yugoslav President that a ground invasion was now on the cards if he did not agree.
When the Serb side broke for internal consultations at about 9.30pm, the Ahtisaari jet was sent to Budapest to re-fuel, and the Finn caught up on his sleep. The reason, he later joked, was that he would be able to look "ruggedly handsome" for the world's press.
If the Finnish envoy was sleeping well, the deal was not yet in the bag. The Yugoslav parliament was due to meet in closed session, but at 1.10pm Mr Ahtisaari was told formally that it had given its approval, as had the federal government that morning.
When Bill Clinton had gone to bed on Wednesday night there were no indications a peace deal was so close. Mr Talbott had given the White House a downbeat account. Mr Milosevic was expected to try to play off the Russians against the Americans, making concessions, then backing away.
Indeed, the week had got off to a sombre start. The US President had spent the holiday weekend in Florida. Public opinion was slipping away, and Mr Clinton tried to galvanise a sense of national purpose and moral outrage.
There was another looming reality: the need to start thinking about what would happen if the air war did not work. A progress review had already been set for Thursday with the Joint Chiefs of Staff and the Defense Secretary, William Cohen, had confirmed that ground forces were on the agenda. At around 6.30am Washington time on Thursday, officials phoned with the news. By 2pm Mr Clinton stood in the Rose Garden and told the press.
Tony Blair and the other EU leaders were posing for their traditional "family photo" at a summit in Cologne when a telephone call bearing the dramatic news from Belgrade came through. That evening Mr Ahtisaari flew into Cologne to a spontaneous round of applause, an unusual gesture of exuberance in such a formal gathering.
Afterwards Mr Cook, joined by the foreign ministers of Germany, France and Italy, went straight to a private room to ring Madeleine Albright. They opened a bottle of champagne to celebrate the deal - although Mr Cook signalled a note of caution by adding some orange juice to his glass. He would drink it neat when the refugees were returned to Kosovo, he said.
Mr Milosevic's decision to accept Nato's terms was, in fact, made a week earlier, the day after the three-way talks in Stalin's dacha. Mr Chernomyrdin had arrived in Belgrade for 10 hours of talks and left "very pleased" with the results. Having been assured Nato troops would not be allowed to move outside Kosovo, the Yugoslav leader accepted the alliance's demands.
If the Serb capitulation was this swift, could peace have come much sooner?
From the outset the diplomatic track moved slowly but relentlessly. Joschka Fischer, the Green and one-time peacenik, now Foreign Minister of Germany, saw he was in an ideal position to influence events. A member of Nato, Germany was an important military player. But it also held other cards, enjoying the presidency both of the EU and of the other group which has emerged as a forum for diplomacy, the G8 group of seven wealthy nations plus Russia. A strategy grew: Germany would try to align the positions of all the big players, thereby isolating President Milosevic. Central to this was the G8 because, as one German official put it, it was crucial "to bring Russia into the boat". Only then would the Serbian leader have nowhere to go.
The other missing part of the jigsaw was a UN dimension, designed to satisfy both Russia and the queasier members of Nato. If Nato, the G8 and the EU could be brought into agreement, the next step would be to encapsulate the terms of a peace settlement in a UN resolution.
The moment when the Russians signalled to the West that they were ready to set aside their anti-Nato theatrics and do business had come in mid- April, with the appointment of Mr Chernomyrdin. Yevgeny Primakov, then Prime Minister and a foreign affairs veteran, was sidelined. The difference between the two was crucial. There were shudders in the West, but little surprise, when TV pictures showed Mr Primakov laughing and joking with Mr Milosevic in Belgrade in the war's early days.
Mr Chernomyrdin, a pro-Western millionaire, was a different animal, and one burdened with far less domestic political baggage. Although he continually called for an immediate end to Nato bombing and insisted on Yugoslavia's sovereignty, he was as impartial a player as Moscow was ever likely to supply.
On 6 May came the first breakthrough when, at a meeting of G8 foreign ministers in Bonn, Russia signed up to the principles of a deal. Within two days, that prospect seemed dead and buried.
Nato's accidental bombing of the Chinese embassy on the evening of 7 May gave the Serbs their biggest propaganda coup of the war and raised the prospect of a veto by Peking at the UN Security Council for any peace plan without an immediate end to the bombing. As the effects sunk in, Russia threatened to pull out. Remarkably, despite fury in China, the crisis subsided within a week, and the diplomatic push resumed. As president of an EU country, but a non-Nato one with excellent relations with Russia, Mr Ahtisaari was appointed as Europe's mediator.
Astonished by the speed of Mr Milosevic's response, Robin Cook was this weekend prepared to admit he is "cautiously optimistic" despite the many unresolved issues. The week before he had told colleagues that the situation in Serbia was like an avalanche "you could see the pressures, you could spot the cracks starting to appear, like an avalanche it could come down tomorrow or it could go on hanging there for two months."
"In the event," he says now, "it did come down."Reuse content