Sir Keir Starmer's premiership has never looked more vulnerable as growing numbers of his own MPs call on him to stand down after a disastrous set of election results.
The prime minister has vowed to fight on, even suggesting he could serve two terms, but the choice could very soon be taken out of his hands.
It is a fast moving and volatile situation, but here are some scenarios on how things might play out in the coming days and weeks.
The Labour backbencher Catherine West surprised everyone on Saturday by announcing that she was prepared to challenge Sir Keir for the party leadership.
She's never had a high profile in the party. But Sir Keir gave her a junior ministerial job in the Foreign Office after Labour's election win in 2024. He sacked her when he reshuffled his government last year.
She has no ambitions to take on the top job herself, but said she had grown frustrated with the apparent reluctance of cabinet members who have been quietly lining up their own bids to launch after Thursday's battering at the polls.
She would need to get the backing of 20% of the Parliamentary party - 81 MPs - to kick off a leadership contest.
So far more than 30 Labour MPs have called for Sir Keir to go but not all of them are certain to back West, as they may feel now is not the right time for a contest.
If West succeeds, the ball is then in the court of Wes Streeting, Angela Rayner or any other Labour heavyweight with eyes on Number 10.
Streeting backed the prime minister on Friday, but did not explicitly rule out standing in any contest. Rayner has issued a 1,000 word statement warning the PM that Labour may be facing its "last chance" to deliver change.
If West gets 60 or 70 MPs backing a leadership contest it might be enough to flush out a challenge from the likes of Streeting or Rayner - convincing them there is appetite among the Parliamentary Labour Party for a change.
It could also put Sir Keir on notice that the party is ready to oust him when they or other leading figures do finally make a move.
Another factor could be cabinet resignations, which as we saw with the previous Conservative government, can be a precursor to a prime minister being forced to stand down.
If West's leadership challenge falls flat on its face, it is likely to shore up Sir Keir's position, in the short term at least.
It would allow the prime minister to claim he has the support of his party - and suggest to would-be challengers that, when push comes to shove, Labour MPs are perhaps not as keen on ousting him as they are saying in private.
This is the dream scenario for some Labour MPs, including West, as it would avoid a messy leadership contest that would look self-indulgent to voters reeling from the ongoing cost of living crisis.
Would senior cabinet ministers sit Sir Keir down and tell him that he needs to stand aside for the good of the party? Would he listen to them?
Would they be able to agree on a unifying figure to take his place, without a contest?
It feels unlikely at the moment, particularly as Sir Keir will know that setting a timetable for his departure would turn him into a zombie prime minister and lead to weeks, or months, of jockeying for position among would-be challengers with all the instability that would entail.
The prime minister is no stranger to relaunch speeches - but the one he is due to deliver on Monday is set to be the most significant of his entire career. If it goes badly, it might the last one of his career.
Labour MPs want to hear that he understands the scale of the difficulty the party is in - and that he has a clear vision for getting them out of it and can convince voters that the government can make a positive difference to their lives.
Last year, when he was already in a tight spot, many Labour MPs felt Sir Keir's Labour conference speech, where he spoke about taking the fight to Reform UK, had been one the best he'd ever given as party leader.
West has said she will listen to what he has to say before deciding to send out letters to Labour MPs asking for leadership nominations.
Then, on Wednesday, the government will set out the new laws it wants to pass in the coming year, in the King's Speech.
Sir Keir will be hoping his party will be gripped by a new sense of purpose and energy, with policies on tackling energy costs and forging closer ties with the EU promised, among other things.
In this scenario, Labour MPs will forget all about changing leaders and rally behind the man who delivered a landslide general election victory less than two years ago.
In this scenario, Sir Keir sees off a leadership contest next week and stays on as prime minister long enough for Andy Burnham to return as an MP to challenge him.
The Greater Manchester mayor - who has made little secret of his leadership ambitions - was blocked from doing just that earlier this year by Labour's National Executive Committee.
His supporters argue that the party's ruling committee would not dare do that again, given the mood in the party, and Angela Rayner has said he should be allowed to return, so that the party has its "best players" In Parliament.
But members of the committee have told the BBC they would block Burnham.
Crucially, this scenario hinges on Burnham finding a Labour MP willing to stand down and trigger a by-election. That hasn't happened yet - and there is also the possibility Burnham finds a seat to contest and is selected as the candidate, but loses.
Given everything the prime minister has said since Thursday's elections, this looks like the most unlikely scenario of all, but at the moment it feels like anything is possible.
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