Roman Catholic cardinals from around the world meet Monday for the last time before they get down to voting.
Tuesday, the 115 cardinal-electors - who will choose the church's next leader - will hold their first vote - but it probably won't be their last.
If two-thirds of the conclave agrees, white smoke will announce that there is a new Pope.
The chimney - the chimney that will announce to the world whether there's a new pope, is placed atop the treasured, 500-year-old Sistine Chapel.
It is delicate work, upholding a tradition where white smoke billowing from the chimney signals a new pope has been named.
"The last thing they want is for the Sistine chapel to turn into a smoke filled room."
It is after all where Michelangelo applied his hand.
A specialized stove and chemicals to enhance the smoke's color, goes along with the chimney.
It does take time for the smoke to go from grey to either white or black.
"One of the bits of drama about a conclave is that the Catholic Church usually is a highly scripted, totally predictable enterprise you know exactly what is going to happen and you know when. But with the conclave all bets are off," John Allen, a CNN Vatican Analyst said.
The conclave, their decision, shrouded in secrecy and tradition, and some modern twists. Electronic jamming equipment ensures no one inside or outside the conclave knows the results before its ready to be announced.
"I'm ready to go home I've run out of socks," Cardinal Timothy Dolan, the Archbishop of New York said.
The race, unlike anything any elected official has ever seen, is on.
The front-runners, out in force in Rome.
There's Cardinal Odilo Sherer of Sao Paulo, Brazil, could he be the first pope of the new world?
One of the front-runners, Cardinal Angelo Scola of Milan, Italy said mass at Rome's church of 12 apostles.
And there's one of the dark horse candidates, Boston's Sean O'Malley. Could he be the first American pope?
"Let us pray that the Holy Spirit illumines the Church to choose a new Pope who will confirm us in our faith and make more visible the love of the Good Shepherd," Cardinal Sean O'Malley, the Archbishop of Boston said.
The public politicking nearly, over, once the conclave starts, the cardinals go into deep seclusion until a decision is made.