In the spring of 2010, Paul McMullan found himself staking out a hoof-marked riding trail alongside some woodland near the country mansion of Rebekah Brooks, his former boss. A veteran Fleet Street journalist who’d spent much of his career at the notorious News of the World tabloid, McMullan was now hunting for a front-page shot: Brooks, one of Britain’s most powerful press players, on horseback alongside David Cameron, the man many pegged as its next prime minister.

Since taking the reins at News of the World a decade earlier, Brooks had risen to become a fearsome operator on the media scene. Now CEO of News International, Rupert Murdoch’s mighty U.K. media arm, she oversaw four of Britain’s most influential newspapers—making her a force for politicians to reckon with. McMullan was acting on a tip for the left-leaning Guardian newspaper that Brooks and Cameron often joined one another for riding jaunts. Local publicans, riders, and dog riders had told him the group could be caught some weekend mornings around dawn. A photo would suggest how Cameron and the Murdoch family’s most trusted deputy were cozying up. “That was the shot that might have changed the whole election,” McMullan says. “It could have encapsulated the idea that David Cameron was molded by the Murdochs.”

McMullan never got his photo (he says he overslept). But the Murdoch newspapers had swung their support Cameron’s way, and he emerged as the new prime minister after hotly contested elections that May. Two years later, his relationship with Brooks has become one of the most contentious topics in the phone-hacking saga rocking Britain. And with Brooks scheduled to take the stand at the public inquiry into the scandal on Friday—amid reports that she’ll release texts and emails between herself and the prime minister, reportedly up to 12 text messages a day signed off with a kiss—Cameron is finding himself increasingly drawn into the middle of the drama.

For Cameron, this threatens to snowball what has been a damaging two weeks into something worse. The Conservative Party was badly battered in Thursday’s local elections; it was announced that the U.K. had slid back into recession; and it was revealed that a senior News Corp. lobbyist may have been inappropriately close to officials in Cameron’s government as the company made a controversial bid for the majority stake in TV giant BSkyB.

What started as a scandal over phone hacking at the News of the World has now become an investigation into what could be an even bigger political scandal: the question of whether a quid pro quo may have existed between the Conservative Party, seeking the support of Murdoch’s four major papers in the U.K., in return for nodding through News Corp.’s $16 billion bid for the remainder of the most lucrative U.K. broadcaster.

Nearly a year since the scandal reached a head, much remains fuzzy about Brooks—mainly, how she was able to rise so fast. Much of the speculation has focused on her relationship with Murdoch, with Brooks deemed an “impostor daughter”  to the 81-year-old mogul. But there seems to have been one undeniable feature of her rise: an uncanny ability to get close to people in power. Nowhere was that more evident than in her relationship with Cameron—which was always a dangerous prospect for any politician, and may come back to bite him in the end.

“She was a formidable enemy to have,” Labour M.P. Tom Watson, who has been leading the campaign against phone hacking in Parliament, tells The Daily Beast. “But even those who liked her knew she was a very dangerous friend.”

Brooks was known to be close with both Tony Blair and his successor, Gordon Brown. They came to her wedding, and she famously attended a sleepover held by Brown’s wife. But sources say Brooks was especially intent on courting Cameron. “Rebekah effectively stalked David Cameron in his constituency home,” is how one Cameron opponent inside Westminster puts it. “The phone would ring all the time, and it would be 'Hi, it's Rebekah.’ She’s brilliant at the networking thing. She didn't just want to be Cameron's friend: she wanted to be his best friend.  It was an aggressive courtship. It was a campaign.”

Cameron was director of public affairs for the powerful commercial TV station Carlton before he was elected to Parliament in 2001, a promising but relatively unknown M.P.  Brooks, for her part, was a regular weekender in Cameron’s wealthy North Oxfordshire constituency, whose honey-colored limestone mansions are just over an hour outside London. As the editor of the highest-circulation English-language paper in the world, with a formidable reputation for salacious celebrity scoops and merciless political exposés, she was a figure any politician would seek to please or pacify.

According to some colleagues, it was not Brooks’s journalistic skill that shone through during her three years editing News of the World, at a time when hacking was rife. “She didn’t understand journalism,” says a senior journalist who lost his job when the paper was shuttered last year. “So she created an atmosphere where things like hacking happened.” McMullan, who was caught on tape by the actor Hugh Grant talking openly about illegal activities at News of the World, first met Brooks in the late nineties, when she was a junior features editor. “She was sweet but out of her depth,” he says. “Most her ideas seemed to come from old copies of Cosmopolitan magazine she’d seen at a doctor’s surgery. She used to congratulate journalists for doing the simplest things.”

Though McMullan has openly accused Brooks and her deputy Andy Coulson of overseeing the phone hacking, he still has a soft spot for her. “She was so hopeless, she made you want to protect her,” he says.

It’s a common refrain among both foes and friends: Brooks evinces a strange mixture of charm and vulnerability. Tactile and open, she makes you feel both important and protective. She shares confidences as if you are the only person she trusts in the world.

McMullan left the Sunday tabloid a year after Brooks became editor, annoyed that she had become “more interested in her celebrity friends” than journalism. But Neville Thurlbeck, who was her news editor then and has since been arrested under suspicion of phone hacking, thinks this was part of her strength. “She had the full skill set,” he says. “Namely, a long list of highly placed contacts who would bend over backwards to help her.”

Those contacts took root. The seeds of what is now called the ‘Chipping Norton’ set, named after the local town in the rolling Cotswold Hills, date back to the late ’90s when PR guru Matthew Freud (great grandson of the founder of psychoanalysis) retreated to a family house there during his reported on-off relationship with Elisabeth Murdoch, who was then pregnant with his child. Brooks soon rented a cottage close to theirs on the Blenheim estate and was on hand for Elisabeth’s bridal shower, and attended the very small private wedding in which the elder Murdoch gave his daughter away.

Even one of Cameron’s biographer’s, the Independent’s James Hanning, says he doesn’t know for sure when Cameron and Brooks first met. The first public record of the Brooks/Cameron connection can be found in the House of Commons Register of Members Interests, which details how Brooks invited Samantha and David Cameron to a lavish World Cup Party hosted by the Beckhams in 2006.

But the relationship is more likely to go back at least a year earlier, to Cameron’s bid to become leader of the Conservative Party. At that point Cameron was a relatively unknown figure, and had held no senior office in government and had only been in the shadow cabinet for a couple of years, but he leapt onto the political stage with an impressively crafted PR campaign and the promise of a detoxified Tory brand. Plausible, articulate, and claiming green credentials combined with a social liberalism, Cameron was billed by the press as an “heir to Blair” from the center right.

In October 2005, Brooks’s close friend and former deputy, Andy Coulson, preempted an exclusive story in a rival paper, the Mirror on Sunday about Cameron’s campaign manager, George Osborne, and allegations of drug taking. Coulson was then editor of News of the World, which ran a "spoiler" on the same day in which Osborne denied the allegations. Months later, one of Brooks’s chief executive editors at the Sun was appointed Cameron’s speechwriter. Coulson would get even closer to the new Tory leader and be appointed as the party’s communications chief just months after he’d resigned from News of the World in the wake of the first phone-hacking trials in 2007. He gives his evidence to the Leveson Inquiry this Thursday, a day before his former boss.

It was Coulson’s appointment, according to one former News International journalist, that seemed to seal Rebekah’s campaign to shift News International from years of Labour support. Until that point, Murdoch had been skeptical of the new Tory leader. According to Murdoch’s biographer, Michael Wolff, who spent hours with the media mogul during this time, “Whenever Cameron was mentioned, Rupert used to screw up his face and mutter dismissively ‘PR.’”

In 2009 on the eve of Prime Minister Gordon Brown’s speech to the Labour Party Conference, the best-selling Sun tabloid changed 12 years of Labour support and in a full-page headline claimed “Labour’s Lost It.” By the time of the 2010 general election, when all four News International newspaper titles had moved to the Conservatives, Brooks was the new CEO, and she had married Charlie Brooks. She moved into Brooks’s family pile, a large manor house only a mile or so away from Cameron’s constituency home. After the new government was formed, Rebekah was reportedly one of a select handful of guests at the prime minister’s private birthday party, otherwise attended by old school and college friends.

A source close to Cameron is known to regale friends with the story of the time he asked the prime minister’s wife, Samantha Cameron, how she and her husband distinguish their real friends from those who have just latched onto them because of their power and celebrity. “Well, there’s x and there’s y and there’s z,” Samantha Cameron replies in the tale. “And then there’s Rebekah ...”

“She courted him like crazy as soon as he became leader,” the source tells The Daily Beast. “It was all one way.” A former News International insider maintains the personal and political were one and the same for Brooks: “She liked to be close to power. It was very personal, but also about power in its purest sense—advancing the interests of the company.”

Since the events of last summer, the influence of the Chipping Norton set as an axis of media and political power seems gone for good. As Mark Borkowski, a rival PR titan to Matthew Freud, explains: “There’s a sort of strange unwritten law that no one talks about it. It’s like Victorian England, when everybody can’t deal with death. It’s not that the Chipping Norton set faded away. It’s now toxic.” But it’s this cozy set of friendships, riding excursions, and commercial and political interests that form the greatest danger for Cameron as Brooks and Coulson take the stand this week.

Rebekah has a new daughter, born in January to a surrogate mother. But she could be indicted on several serious charges and could well be facing prison time. The allegations against her have gotten so serious, and the coverage and vitriol so intense, that many are worried she’ll argue she can’t get a fair trial in Britain—and indeed, the human-rights lawyer she hired to help her defense published an article in the Telegraph recently arguing exactly that.

Brooks has been arrested and interviewed on suspicion of three different offenses—phone hacking, payment to police officers, and suspicion of conspiracy to pervert the course of justice. Police files in the case of the latter suspect offense have been passed to the Crown Prosecution Service, but no charges have been made against Brooks yet. Anything relating to possible criminal charges cannot be discussed at the Leveson Inquiry, in order not to prejudice any future trials. On Friday this week Brooks's networking with politicians will be the main theme—and more than anyone Cameron will be in the dock. The cross questioning has already begun.

Only two months ago, the revelation that Brooks had been loaned the use of a retired Metropolitan police horse caused Cameron to derail a press conference during an important EU summit, and admit he had ridden the horse in question, Raisa, which was reportedly returned to the Met in poor condition in 2010. The image of the prime minister out “hacking” with a knackered old mare was a gift enough for cartoonists and satirists, but Cameron was careful to emphasize his friendship with Rebekah’s new husband, the former racehorse trainer, Charlie. Cameron pointed that they were old school chums from Eton, Britain’s most elite private school.

But as a senior Tory explained, “Cameron and Charlie were four academic years apart at Eton, and in different houses [halls of residence]. It’s highly unlikely they ever knew each other.” Riding in Britain is generally associated with the landed gentry and for David Cameron, whose Conservative-led coalition government is increasingly perceived as privileged (there are eight old Etonians in the cabinet), the image of him consorting with an old boys’ network on horseback was hardly welcome. But it was better than the alternative—a picture of the prime minister out riding with the former Queen of Fleet Street, Rebekah Brooks.

—With Mike Giglio in London