Hundreds of thousands of Egyptians are expected to take to the streets Friday, united in a call for "freedom" and "dignity" and the end of the regime of President Hosni Mubarak.
After three days of widespread protests that have left at least seven dead and about 1,000 arrested, protest organizers have designated this the ultimate "day of rage."
There is much riding on the outcome. How many people turn out, how the police deal with them and whether the army takes control - all of these things will determine the future of the current regime.
Arriving in Cairo Thursday evening, Mohamed ElBaradei, the Nobel Peace Prize-winning former head of the international Atomic Energy Agency, made clear his intentions.
"It's a critical time in the life of Egypt, and I have to participate with the Egyptian people," said Mr. ElBaradei, who has considered running for president in elections this year.
"If people, in particular young people, if they want me to lead the transition, I will not let them down," he said.
Clearly the country is worried about what may transpire. Trading on the Cairo stock exchange was halted Thursday morning when the value of the market fell more than 9 per cent in the first 11 minutes.
Safwat El-Sherif, secretary-general of the ruling National Democratic Party, tried to put a brave face on things when he gave the party's first public response to recent events at a hastily called news conference.
"The NDP is ready for dialogue with the public, youth and legal parties," he said. "But democracy has its rules and process. The minority does not force its will on the majority."
Regardless of the outcome of the protest, this popular uprising represents a new reformist movement in Egypt, one not linked to the traditional centres of opposition in Egypt - the pockets of liberal intellectuals and the Islamists who have been successfully marginalized by the 29-year-old Mubarak regime.
At its core is a disparate group of mostly secular young people drawn from most walks of society and politics. Some are holdovers from the Kefaya movement that demonstrated for democracy starting in 2004. Others hail from the April 6 youth movement that organized protests in aid of striking workers in an industrial town outside Cairo in 2008. Many are completely unaffiliated.
Maryam Suleiman, a 20-something wearing blue jeans, was hoarse from leading the down-with-Mubarak chants on the steps of the Journalists Syndicate near the national courthouse Thursday. She and 75 fellow demonstrators stood face-to-face with the 150-or-so security forces lined up against them.
Ms. Suleiman, who describes herself only as "a citizen," says she belongs to a little known movement called the Popular Front for Peaceful Change.
Mohamed Gamal is one of Egypt's pre-eminent bloggers, who goes by the handle "Gemyhood." At 30, Mr. Gamal describes himself as one of the oldies in the protests. It all started with a small group of bloggers who got together five years ago, he said.
"We were dreaming of democracy and new governments," he explained, and began to realize the potential of the Internet. "We were the first to use Facebook, the first to use Twitter," he said, in order to get out messages and bring in new people.
"Things are moving very fast in Egypt, and this is the only way of keeping up with the people."
This diffuse resistance movement has sprung up without the help of the traditional opposition - liberal reformers and the Muslim Brotherhood - and it represents a different constituency with its own agenda.
"We've gone way beyond the old movements," Mr. Gamal said. "Even Kefaya is too old now."
"Ours is not a political movement," Mr. Gamal insisted. "It's people power, unaffiliated people power."
The goal that started out as democracy and political change, has simply become the end of Hosni Mubarak. "We want to take this man down," he said.
The secular youths out in the streets seem brave and desperate, but also completely clueless about how to take what they're doing and convert it into a viable governing force.
Mr. Gamal admitted he does not know what the protesters will do if they succeed. "We haven't thought that far ahead. But the Tunisians didn't know what was going to happen when they started their protests either."
Nor does he worry whether there any leaders among the group. "We don't care about a leader," he said. "They're all part of the elite and we don't want any part of that.
"We don't trust [Mr. ElBaradei]either," he added.
Finally, Mr. Gamal admitted he does not exactly understand the forces he's messing with. "Things are now out of control."
Watching anxiously on the sidelines this week has been the Muslim Brotherhood. For more than 80 years the Islamist movement has been the social conscience and chief opposition to the powers that be. They have no desire to be shunted aside just when that power may be compromised.
After declining to officially participate in protests earlier this week, the Brotherhood announced it would take part in Friday's massive protest marches.
"We are joining the parade," said Mohamed Beltagi, a candidate in the last election, "not at the front, not at the back, but in the middle."
Being at the front would give security forces a reason to use even more violence, he explained.
Does the Brotherhood feel threatened by this more spontaneous uprising? "Not at all," Dr. Beltagi said. "We all want the same thing. This protest shows that it's more than the Muslim Brotherhood that wants freedom and dignity."
However, at least 20 members of the Brotherhood were arrested late Thursday night and early Friday morning, its lawyer Abdelmoneim Abdel Maqsoud told AFP.
Among those arrested at their homes were five former members of parliament and five members of the political bureau, whose best known leaders are Essam El-Eriane and Mohammed Moursi.
At the end of the day, Egypt's army is likely to hold the trump cards. Will it fire at the youthful demonstrators?
"No way," Mr. Gamal said. "We love the army. It's the army that's going to step in and protect us from the police," he said.
Indeed, in 1968, that exactly what they did when dealing with large-scale student riots. When ordered to intervene, the army commander ordered his men to empty their weapons and carry no ammunition. Order was restored without a shot being fired.
The army, the protesters hope, doesn't want Egyptian blood on its hands.