Two chess grandmasters have spent November locked in stalemate, with the world chess championship up for grabs.
After 11 games and 11 draws, American Fabiano Caruana is seeking to take the title from Norwegian Magnus Carlsen.
The final match takes place on Monday – but another draw would begin a series of fast-paced tie-breakers, culminating in a game type known as “Armageddon”.
If he wins, Caruana would be the first US world champion since Bobby Fischer in 1972.
But he has faced a fierce title defence from Carlsen, who has been champion since 2013 and is the top-ranked player in the world.
On top of the prestige that comes with the title, the pair are also battling over a €1m (£880,000) cash prize.
The 11-draw series in London makes it one of the most fiercely contested in history – never before have so many games ended in a draw, much to the disappointment of some keen chess fans.
Awarded half a point each for every draw, the score is 5.5 to 5.5 in this best-out-of-12 format.
If they draw all 12 games, the tie-breaker is a series of increasingly fast games on Wednesday.
In the ordinary games, each player starts with a generous time bank of 100 minutes, and more time is added as the game progresses. That means it is possible to watch a grandmaster do nothing except stare at the board for several minutes.
But in the tie-breakers, four games are played with just 25 minutes on the clock, and 10 seconds added after each move.
If it is still a draw after that, two “blitz” games are played – with just five minutes per player and three added seconds per turn. In such circumstances, mistakes are much easier to make.
In the unlikely event that after two sets of blitz, the title is still tied, a sudden death variety called “Armageddon” is played.
In this chess game type, there will be a winner – a draw means a victory for the player wielding the black game pieces. To compensate, white gets more time on his clock – a minute more, but the pace is still as fast as a blitz game.
The match begins at 15:00 GMT, and is being live-streamed by popular gaming broadcast site Twitch.tv and on chess.com.
Source BBC News