In every revolution, a moment comes when the beleaguered leader loses control and a metaphorical trapdoor opens beneath his feet.
For Viktor Yanukovych, it came when his enemies became masters of Kiev and guardians of every branch of his government.
The Ukrainian President's own office was guarded not by the police but a knot of protesters clad in motley camouflage and green helmets.
These were the very men scorned by Yanukovych as "bandits" and "Nazis", and yet they were the new sentries beside the wrought iron gates through which he had swept in the presidential Mercedes as recently as Saturday. Other protesters guarded the cabinet building and Ukraine's Parliament. The chamber was in noisy session, firmly under the control of the opposition, and busily voting to impeach Yanukovych and release one of his foremost enemies: Yulia Tymoshenko, the former Prime Minister who was jailed in 2011.
As for the President's security detail, they appeared to have been pragmatic enough to change their loyalties.
Colonel Mykolai Kolodayzhni, the deputy head of security for the presidential administration, said he was willingly co-operating with the protesters. "We have found words which each side can understand. Life continues, we should work and we should live," he said.
When the protesters arrived on Saturday, they were not exactly welcomed, but nor did anyone try to stop them. Only the day before, snipers had shot dozens of these people in cold blood just around the corner in Independence Square.
By that time, it appears that Yanukovych had already left Kiev and flown to the town of Kharkiv in his old stronghold in eastern Ukraine. The permafrost around Ukraine's confrontation had finally cracked and powerful men made a series of crucial decisions.
First, the agreement painstakingly negotiated by Yanukovych and three opposition leaders, with the mediation of the foreign ministers of Poland, France and Germany, was quietly scrapped. In the space of five hours, the President buckled and chose to flee; his security chiefs resolved to co-operate with their enemies; and the protesters themselves seized their chance to advance from Independence Square and take control of the key institutions of the state.
By midday on Saturday it was all over, carried out bloodlessly and with relatively little drama. The police simply melted away.
Kolodayzhni made clear that his boss, the head of security for the president, had been kept fully informed. The superior officer had apparently raised no objections to handing over the nerve centre of Ukraine to "bandits" and "Nazis". But the protesters were not ill-disciplined thugs. After his flight from the capital, no one broke into his office to ransack the contents or smash up his portraits. No graffiti appeared on the wall outside.
Yesterday, there was not so much as a shattered pane of glass at any of the public institutions under the demonstrators' control. The protesters simply assumed the role of polite sentries.
"We are working in full co-operation with the state security whose professional duty is to guard these buildings," said Ostep Kryvlyk, who styled himself "international secretary" of the protest movement's "self-defence units".
"We as patriots believe that this property belongs to the nation and therefore it is to be preserved from any kind of intervening for the next president and the next government."
A city that had been silent and fearful began to shake itself back to normality.
"It's like a dam," said Volodymyr Badnar, a 25-year-old protester. "The water was rising and rising and then people started dying for their freedom and that was the end for this dam."
Yanukovych appeared on television from an undisclosed location. Defiantly, he insisted that he would not resign and claimed to have fallen victim to a "coup d'etat". Within the hour, Ukraine's Parliament had delivered its resounding answer, deciding to impeach him by 328 votes.
But there was no mood of celebration. No one in Kiev can forget the terrible human cost of this revolution, with 29 people shot in the streets on Friday alone and perhaps 70 killed in the past week.
Once again, tens of thousands massed in Independence Square, known to all as the Maidan. This time they gathered not to protest but to mourn the dead.
As a third coffin passed and then a fourth, a chant of "Glory to Ukraine!" rose from the stage. But many of those in the throng were too overcome by grief to respond. After months of toil and struggle, their revolution had succeeded. But the price of victory was so great that it felt indistinguishable from defeat.