The sensational prospect of only the second-ever defection of a Labour MP to the Conservatives is the culmination of a saga of sex, revenge and skullduggery.
With her auburn corkscrew curls, Jane Griffiths cuts an exotic figure in the midst of the ranks of grey-suited men to be found propping up Westminster's bars. Elected in 1997, she epitomised the group of "Blair babes" that carried Tony Blair to Downing Street. A translator at GCHQ, the skilled linguist was just the sort of reliable, professional married mother-of-two New Labour was desperate to attract.
At first her parliamentary career promised to flourish as she loyally followed the party line, but then came a now notorious MPs' trip to Kosovo in 2001.
A lurid tabloid report, alleging how a fellow female MP had indulged in "inappropriate behaviour" with a Royal Marine captain, landed her an interview with the then Chief Whip.
"Wherever you go there seems to be trouble," concluded Ann Taylor after Ms Griffiths admitted telling other MPs about what she alleged had happened on the bunk below hers.
It was her feud with Martin Salter, the MP for Reading West, that set the seal on her fate, however.
The pair, both councillors before being elected to the Commons on the same day, were once close. Mr Salter, a former lorry driver and airport baggage handler, and Ms Griffiths, who speaks four languages, even considered sharing a Westminster office.
Somewhere along the line, however, the two had a spectacular falling-out. A taste of the animosity is given by Ms Griffiths's allegation that he had once said to her: "You are fucking menopausal."
"Yes, I am 49, but it is still pretty unfair," she said earlier this year.
Mr Salter denies the claim.
In 2002 police were called to her office when, after a break-in, her computer appeared to have developed a fault that prevented access to its files.
By now the de-selection net was closing in. Tony Page, a PR executive and friend of Mr Salter, mounted an ultimately successful challenge to become Labour's parliamentary candidate in the forthcoming general election.
The rancorous atmosphere was made worse by the fact that Mr Page's previous convictions for indecent behaviour were made public in the middle of the fight.
Mr Page, who is gay, was forced to say that he had been convicted of behaviour no worse than that found in a Coronation Street plot line.
If Labour thought that they had seen the last of Ms Griffiths when she was deselected in February, the following Sunday's newspapers brought a most unwelcome surprise.
In an interview in the Mail on Sunday she made a series of extraordinary allegations of bad behaviour by Labour MPs and ministers, including the claim that that she had been the victim of an attempted sexual assault by one MP.
In unforgiving detail she also painted a picture of drunkeness among her Westminster colleagues.
"I have seen government ministers falling down drunk. I have seen one in Soho being held up and poured into a taxi."
She told of one incident in which a minister had to be dragged feet first from the lavatory after having passed out.
Still the feud with Mr Salter continued, however. Ms Griffiths used House of Commons privilege to accuse her neighbour of sending a racially inflammatory letter to her constituents.
Ms Griffiths, still a Labour MP, holds a trump card in her dealings with a by now exasperated party: she knows that by resigning she can trigger a by-election at any time.
On Tuesday, however, a piece appeared in the Independent diary that seems to have led her to choose an altogether more dramatic final chapter for her parliamentary career.
It reported that Hilary Armstrong, the Chief Whip, was now considering expelling her from Labour for allegedly briefing a Tory councillor against Mr Salter.
Colleagues say that it was the final straw. In March Ms Griffiths admitted that she had been approached by both the Tories and the Liberal Democrats.
She said then that she would be sticking with Labour. In words she may come to regret, she said: "I could never be a Tory because they have a dark side. You don't see it in public but you know it is there."
She added: "My heart is with the Labour Party. I can't cut it out of me."
This weekend Ms Griffiths is starting a holiday in Africa, a safe distance from the furore her threatened defection will spark in Westminster.
What will happen when she returns is not yet entirely clear, but the least-likely option of all is that she will get the personal call from Mr Blair that appears to be the price of her loyalty.
A brief history of defection
The roll call of those who have defected in the last 100 years is one of both honour and dishonour.
The most famous, and arguably successful, floor-crosser is Winston Churchill, who cheerfully admitted that he had not only "ratted but re-ratted".
Rather less illustrious are the defections of Sir Oswald and Lady Mosley from Labour to the fascist New Party in 1931.
In modern times a defection has been seen as a weather vane, showing the prevailing political wind.
Reg Prentice's resignation of the Labour whip in 1977 to serve as a Tory heralded the rise of Thatcherism.
The mass defection of 26 Labour MPs and one Tory in 1981 that saw the birth of the SDP seemed at the time to spell the end for the Labour Party.
By the time Alan Howarth left John Major's government in 1995 to rally to the standard of Tony Blair, however, it was clear that it was back with a vengeance.
The ascendancy of the new political order was confirmed when Shaun Woodward crossed to Labour in 1999.
If Ms Griffiths does defect to the Tories, it is bound to be seen as further evidence that change is in the air.Reuse content