The odds on Keir Starmer leaving his post as Labour leader this year drifted to 7.06/1 after Labour caused an upset by winning the Batley and Spen by-election.
On Thursday afternoon, with voting well underway, the Tories were trading at 1.192/11 on the Exchange to take the seat from Labour who were out to 6.25/1. In the early hours of the following morning, it turned out Labour had won by 323 votes.
Their majority was reduced from 6.7% in 2019 to just 0.9%. And yet in the Yorkshire constituency you could probably still hear the sigh of relief emanating from Starmer's north London home.
While Labour's vote was down, so was the Conservatives'. George Galloway appeared to take votes from both parties. He had previously taken seats from Labour in east London and Bradford with his strategy of rocking up in places with which he had no connection and exploiting local divisions. His plan in Batley and Spen was not to win - his Workers Party of Britain were 75.074/1 on polling day - but to split the vote, handing the seat to the Tories and imperilling Starmer's leadership. It backfired.
By-elections show Tories far from dominant
It was another by-election upset, to go with last month's in June where the Tories were overturned at short odds by the Liberal Democrats - a result that raised questions about the future of the party in the south east of England.
In the north, suddenly the Tories' plan to paint blue the entire red wall looks less assured than it did after they took Hartlepool in May.
Batley and Spen, Chesham and Amersham and Hartlepool are all very different places with distinct demographics. But the fact remains that the Tories were backed to win all three and in the end they won just one.
In Kim Leadbetter, the sister of the murdered MP Jo Cox, Labour had a candidate in Batley and Spen with a unique and enduring connection to the constituency. Matt Hancock's affair, news of which broke the week before the by-election, may have also hurt the Tories. Perhaps they thought it would not, as allegations of sleaze hadn't cut through in Hartlepool. If so, Boris Johnson's Tories aren't as electorally shrewd as some have claimed.
They still have an 80 seat majority in parliament but Paul Krishnamurty was right to argue on this site that Tory dominance was not all it had cracked up to be.
They are 2.111/10 to win a majority at the next general election while a hung parliament is 2.427/5.
Victory buys time for Starmer
They'd never admit it now, of course, but the likes of Andy Burnham 3.412/5 and Angela Rayner 7.26/1 - the leading candidates to be Labour's next leader - were probably working out what to say on Friday morning in the event of another by-election defeat.
On Thursday, Rayner denied she was planning a leadership bid, although there were persistent claims that MPs had been sounded out about supporting her. Burnham, meanwhile, has been subtly undermining Starmer ever since Labour's defeat in Hartlepool.
For what it's worth, I think the prospect of another shot at the leadership (he previously stood for it in 2010 and '15) has gone to Burnham's head and I don't trust him as a market jolly.
It remains to be seen how his leadership bid would come about (he'd need to be an MP). In his recent spat with Nicola Sturgeon, the Mayor of Greater Manchester sounded less like he was standing up for the people who elected him than bolstering his own public profile.
Both Burnham and Rayner will have to get behind Starmer in the short term as he tries to build on Thursday's win. That's one reason we've seen the odds drift on him going this year. But the market doesn't exactly indicate long term confidence in the Labour leader.
He's 3.02/1 to go in 2022, only marginally longer than the 2.186/5 on him making it to 2024 or later. The circumspection is understandable as UK politics becomes more eventful by the year, throwing up the kind of surprises we saw on Thursday.