While she was still chief executive of News International and the 'fifth daughter' of the Murdoch clan last week, Rebekah Brooks wrote to Scotland Yard offering to be interviewed as a witness in its intensifying investigation into the phone-hacking scandal.
The extent to which the fortunes of the former editor of The Sun and the News of the World have been transformed in the space of 72 hours was underlined at midday yesterday when she arrived at a London police station in the expectation that she would be helping police with their inquiries - only to find herself under arrest.
A spokesman for Ms Brooks said she was "surprised" to be formally detained by detectives from Operation Weeting, the inquiry into phone hacking, and Operation Elveden, the investigation into alleged bungs paid to police by journalists, on suspicion of conspiracy to intercept voicemails and alleged involvement in corrupt payments to officers.
The Yard contacted Ms Brooks, who has spent more than half of her life working for Rupert Murdoch's News International, on Friday - the same day her resignation as the head of Mr Murdoch's British newspaper group was finally accepted.
News International sources said the approach was made only after the decision about Ms Brooks' future had been taken and therefore had no impact on her departure.
It is understood she had signalled her readiness to talk to Weeting when it was launched in January. But there can now be little doubt that the Weeting and Elveden detectives believe she can offer them significant help with their efforts to discover the extent to which executives at the NOTW had knowledge of phone hacking at the paper - and who at NI might have authorised alleged payments to police officers.
Among the first questions likely to have been put to her in the police interview room yesterday would have been her knowledge of the single most damaging disclosure in the hacking saga: the eavesdropping and deletion of the voicemails of the murdered schoolgirl Milly Dowler, which caused her parents to believe she might still have been alive.
The hacking, allegedly carried out with the assistance of the NOTW's contracted private investigator Glenn Mulcaire, took place in March 2002 when Ms Brooks was editing the title.
The Independent has established that Ms Brooks was aware of private investigators and some of their services.
In 2001, she commissioned another private detective, Steve Whittamore, who was later convicted of data protection offences, to obtain a 'mobile conversion' by reverse-engineering a mobile phone to obtain details of its registered keeper.
But Ms Brooks has strongly denied having any knowledge of the activities of Mulcaire, who was jailed for accessing the mobile phones of members of the royal household. In an email to NI staff following the disclosure of the hacking of Milly's phone, she said: "I hope you all realise it is inconceivable that I knew [of] or worse, sanctioned these appalling allegations."
In this regard, Ms Brooks' position has been similar to that of her friend and former deputy Andy Coulson, who resigned as NOTW editor in 2007 following the conviction of Mulcaire and was himself arrested by Weeting and Elveden officers this month.
Mr Coulson played a key role in the another matter that police will want to ask Ms Brooks about. He was beside her when she gave evidence as editor of The Sun to the Commons Culture Committee in 2003, telling MPs: "We have paid the police for information in the past."
Asked if she would do it again, she began to answer: "It depends..."
Moments after the statement, Mr Coulson, then editor of the NOTW, intervened to offer assurances that both papers "operate within the [industry] code and within the law". Earlier this year, Ms Brooks said she was not aware of any cases of payments to police. But internal NI emails appeared to show that payments had been made to police officers by NOTW journalists.