Liz Truss has resigned six weeks after she became prime minister.
Tory MPs have been openly plotting over the best way to get rid of her, with events speeding up considerably over the last week.
In the resignation statement, Truss announced that her replacement will be elected within a week.
That means MPs themselves will have to somehow choose a candidate they can all rally round - not an easy task in a party which is tearing itself apart.
Here, HuffPost UK looks at who could replace the PM if she is ousted.
Rishi Sunak
Just weeks after losing out to Truss in the last Tory leadership campaign, the former chancellor is now the bookies’ favourite to succeed her in Number 10.
Supporters of the Richmond MP point out that he rightly predicted that Truss’s plans to borrow to fund tax cuts would lead to economic chaos, and say that’s all the proof you need that he is now the right man for the job.
One Sunak supporter told HuffPost UK today that he will definitely run - and that MPs who had previously backed Truss are ready to back him this time.
However, many of his parliamentary colleagues still blame him for Boris Johnson’s downfall, which was triggered by Sunak’s resignation as chancellor.
One cabinet minister said: “The fact that he’s supported by Dom Cummings tells you all need to know about Rishi.”
Ben Wallace
Reports this morning suggest support is building among MPs for the defence secretary, who is well-respected across all wings of the party, to step in as prime minister.
The fact that he was a Remainer is cancelled out in the eyes of many by the fact that he remains a close ally and supporter of Boris Johnson.
Wallace considered standing for the leadership after the former PM resigned, but decided not to. However, he has never ruled himself out of going for it at some point in the future, and he may see this as the best chance he’ll ever have to get the keys to Number 10.
Kemi Badenoch
The international trade secretary performed well in the last leadership contest and is thought to be taking soundings from colleagues as to whether she should run again.
Badenoch is on the right of the party and was championed last time round by Michael Gove, who could use all of his political guile to help her secure the top job.
Penny Mordaunt
Although she lost out in the last leadership election, Mordaunt almost made it to the final run-off against Sunak and still retains strong support among Tory MPs.
The Commons leader announced she was running again within 10 minutes of Truss announcing her resignation, saying it was “make or break time” and only she can win the next election for the Tories.
Some want her to join forces with Sunak to form a “dream ticket”, with one of them PM and the other their deputy, in a bid to unify the parliamentary party.
But one Tory adviser said many MPs think Mordaunt, who is now Commons leader, “sold out by taking a job from Truss”.
Nevertheless, she is sure to be a strong contender should a vacancy at the top arise.
Suella Braverman
Another one who stood, and lost, in the last leadership election, Braverman has not given up hope of claiming the top job.
An unashamed right-winger, she has already clashed with Liz Truss over immigration, a trade deal with India and drugs policy since being appointed home secretary last month.
Her only chance of winning next time, however, would be if Tory members were given a say, as the party rules currently dictate.
But as one former cabinet minister observed: “If you make the rules yourselves, you can easily change them.”
Grant Shapps
Just a day after becoming the new home secretary, Shapps is now being touted as the elusive “unity candidate” who could bring the Tories’ warring factions together.
It would be a remarkable turnaround for the Welwyn Hatfield MP, who was sacked from the cabinet just last month when Liz Truss became prime minister.
Famed for his love of spreadsheets, Shapps would be able to spot rebellions and plots a mile off, something which would come in very handy if he gets the keys to Number 10.
Er ... Boris Johnson
Almost unbelievably, there is a chance that the Tories could end up turning to the man who only left Downing Street last month.
Despite being forced to quit as PM in disgrace, Johnson himself - and his supporters - believe he is destined to be back in 10 Downing Street one day.
Even by recent political standards, though, it would be an almighty shock were it to happen so soon.