In these turbulent times, most financial pros, even heavyweights, would kill for a Rolodex like Ellyn McColgan's.

Soon after quitting her post as president of Fidelity's distribution and operations unit last August, she began meeting with old contacts and considering her next move. High on the list was James Gorman, at the time Morgan Stanley's chief of wealth management. In October, she had lunch with Gorman in the private dining room at Morgan's imposing Times Square headquarters, complete with an introduction to Morgan chief John Mack. A mere six weeks later, when Gorman was promoted to co-president of the firm, her name went on the short list of possible replacements.

"That day...he called me and said, 'I think we need to talk,' only this time we actually had something to talk about," McColgan recalls. Within four days McColgan was back in New York, meeting with more top Morgan executives. Two weeks later it was official: She took over from Gorman as president and chief operating officer of the Global Wealth Management Group.

The whirlwind hiring took even McColgan by surprise. "Sometimes it's funny. You're not looking to make something happen, and then all of a sudden the opportunity presents itself and you just know that that's the right thing to do," she says.

It was a move few would have predicted last spring when it appeared that McColgan's stellar rise up the ranks of mutual-fund giant Fidelity had positioned her as a serious contender to succeed 77-year-old Chairman and Chief Executive Officer Ned Johnson. Indeed, McColgan could make an impressive case to take the helm of the behemoth buy-side firm. Her track record as the head of Fidelity's brokerage unit included doubling assets under management to $1.7 trillion, as well as increasing the number of client accounts 40%, to 17.1 million. End result: Fidelity is now the largest brokerage house in the country by either measure.

Moreover, her attention to detail and accessibility impressed clients. Harold Evensky, president of Coral Gables, Fla.-based Evensky & Katz Wealth Management, said his firm held a portion of its $550 million of client assets under custody at Fidelity. "She clearly had a very senior position and we...didn't have a huge amount of business with them. It impressed me that she treated my firm and me personally as a very important client," he says.

In April 2007, McColgan was promoted to president of distributions and operations at Fidelity, which essentially put her in charge of nearly half of the firm's 42,000 employees and had her reporting directly to Johnson. Jim Lowell, editor of the independent Fidelity Insight newsletter, says she was well regarded by her staff. "I've heard from people in different divisions that she was a tough-minded but fair boss," he says. "She's an exemplary leader [and] really is a drover [one that drives cattle or sheep] where most people are part of the herd mentality."

Her promotion stirred rumors that she was next in line for the top job. But those were quelled when Johnson, in an apparent effort to stem Fidelity's decline against rivals American Funds and Vanguard, brought in former Fidelity executive Rodger Lawson as president of FMR Corp., which runs Fidelity. Johnson told McColgan she would report to Lawson. "The reason she left Fidelity as quickly as she did, and in a huff, was a direct result of not being given the reins to take the company forward," Lowell says. "It was professionally and personally insulting to her, given the job she had done."

So, after 17 years at Fidelity, McColgan bolted—and started considering her next move. She had met Gorman a few years earlier, when they both served on the board of the Securities Industry Association, and they soon built a rapport. "We met at one of the cocktail parties...and we were chatting and it seemed we wound up on the same side of most issues," she says. "We just gravitated toward each other at meetings to make sure we would say hello and catch up." With Gorman as chairman of the board and McColgan as vice chair, they oversaw the 2006 merger of the SIA with the Bond Market Association to create the Securities Industry and Financial Markets Association (SIFMA). McColgan became co-chairman in 2007.

Still, McColgan says she didn't have any inkling about what was in the offing when she lunched with Gorman last fall. When the opportunity arose to return to Wall Street and work with Gorman, though, it proved too much to resist. "I worked with the same person at Fidelity for 15 of my 17 years," she says. "Knowing who I would work for again was very important to me."