WASHINGTON — Paula Reid, the new Secret Service boss for the South American region, was in Cartagena, Colombia, preparing for the president’s visit when she received an urgent report: A prostitute, upset because she said she had not been paid by a Secret Service agent, had created a disturbance in a nearby hotel, knocking on doors and yelling in the hallways at daybreak.

With roughly 24 hours left until President Barack Obama was due to arrive in town, she instructed her staff to swoop into the Hotel Caribe midday on April 12 and inspect hotel registration records for all Secret Service employees. The Miami-based Reid, who had been staying at a nearby hotel, swiftly rounded up 11 agents and officers and ordered them out of the country. She alerted her superiors that she found early evidence of “egregious” misconduct involving prostitutes, and set in motion the public uncovering of the most wide-reaching scandal at the agency in decades, according to government officials involved in the case.

It fell to Reid, 46, to ride herd on a rowdy group of male colleagues, including two who were assigned to supervise the group, the morning after a drunken bender, according to the officials. While the sordid and salacious details of the men taking prostitutes to their rooms is now well-documented, less is known about the role played by one of the agency’s highest-ranking African-American women in making the clock-ticking decision to replace them on an assignment for which there is no room for error.

For Reid, the moment was not without risk, opening her to a potential internal backlash for ruining the men’s careers and, once the news became public, embarrassing an agency that prides itself on maintaining a stoic public face. Officials familiar with the probe said Reid had the director’s endorsement in the swift steps she took to handle the matter, but some agents said another senior manager might have been less aggressive.

Those who know Reid said the move revealed a steely resolve that has marked her 21-year rise through the ranks of an agency whose macho reputation has again come under scrutiny. Her story offers a counterbalance to critics who contend the Secret Service has been slow to clean up its act from the “Mad Men”-era days when some agents joked their off-duty mantra was “wheels up, rings off.”

Not that Reid, an intensely private person, would admit it. In an interview, she offered few new details of her role, sticking to what colleagues described as her businesslike approach.

“I am confident that as an agency we’ll determine exactly what happened and take appropriate action,” she said, in an interview with her and an agency spokesman. “Despite this current challenge facing the Secret Service, my job is to keep Miami personnel focused on our core protective and investigative missions. Anything less is counterproductive to the many critical functions we perform each day.”

Now, Reid is still in the thick of it, assisting in the ongoing investigation. Those who have worked with her since she joined the Secret Service in 1990 described her as well suited for the challenge.

One former agent who worked with Reid in Miami during her previous stint in that bureau said she was exacting in the extreme, able to quote the agency administrative manual the way “fundamentalists quote the Bible.” This ex-colleague said he did not always agree with her management approach, but he respected her work ethic and ability.

“If every boss was Paula Reid, the Secret Service would never have a problem,” the former agent said. “It would be a lot more boring, but never a problem.”

Reid “is the epitome of what a female agent should be,” said another current agent who also has worked with her. “I wouldn’t be surprised if she becomes director one day.” The agents declined to be named because they were not authorized to speak about her.

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Reid has never married, but describes herself as very close to her siblings, including her twin sister, and her family, most of whom live in the Maryland suburbs.

Tall and lean, she is regularly seen at the gym at 5:30 in the morning and at her desk by 7 a.m. She is always serious when on the job, the former agent said.

After growing up in Calvert County, Md., Reid graduated from the University of Maryland and joined the Secret Service at age 25 after visiting an NAACP job fair that sought to encourage minority applicants for law enforcement jobs.

According to a promotional interview years later that Reid granted to help recruit more female agents, she studied criminal justice in college and was debating whether to go to law school or become an investigator when she chose the service.

“I can’t imagine not being in law enforcement,” she said then, according to her interview, published in an online newsletter,”Women for Hire.”

But Reid’s time in the agency hasn’t always been rosy.

Ten years after entering the service at the bottom rung, she joined as a plaintiff in a class-action lawsuit that claimed the agency engaged in racial discrimination against African-American personnel. She provided a declaration giving examples of ways black agents were relegated to lesser assignments. In the broader suit, some of the plaintiffs contended that senior managers had often used racial epithets to describe criminal suspects but were not reprimanded for their comments.

She eventually withdrew from the case, which continues but has since dwindled to a smaller number of plaintiffs. Still, as a black woman, Reid stood out in a mostly white male agency.

“The general public is intrigued to see a black female in my position,” she said in the “Women for Hire” interview. “They always need to confirm that I really am a special agent. I enjoy being a role model for women and minorities.”

In a separate 1997 USA Today interview about the Secret Service’s desire to recruit more female agents, Reid was quoted as saying that when she and male agents were working together on an assignment, their managers would usually ignore her in favor of her male counterparts.

Until the perception of agents as big, bulky men changes, Reid said at the time, women have to “learn not to take it personally.”

Whatever the challenges, Reid has earned a steady stream of promotions. After spending time as a special agent on the Presidential Protective Detail, Reid joined management as a supervisor in the Miami field office in 2004, overseeing administrative duties. In 2007, she was summoned back to Washington, where she had two prominent jobs in the next four years.

She was special agent in charge of the Protective Intelligence and Assessment Division, which ensures that threats to the president and other officials are identified and carefully monitored, and she was deputy special agent in charge of the Presidential Protective Division and oversaw the White House complex and access to it in the middle of Obama’s term. That included responsibility for overseeing protection for the East Wing, coordinating events and regular contact with first lady Michelle Obama and her family.

Reid’s most recent promotion, earlier this year, was to the highly coveted position of top boss of the Miami office, a division of more than 150 employees that rivals the Los Angeles and New York offices in prestige among national bureaus.

Her move prompted grumbling among longer-serving white supervisors that she was unqualified, according to people with knowledge of the situation.

This month, Reid headed to Cartagena to serve as liaison between the dozens of agents and officers representing several divisions of the Secret Service and other local governments and U.S. agencies involved in preparing for the president’s visit, Secret Service officials said.

Even under ideal circumstances, such a job is a headache of tight scheduling within a vast operation that includes several hundred personnel in a foreign country. But two weeks ago, when Reid took the call that would set in motion a frantic chain of events before Obama’s arrival in Cartagena, some said they could have predicted this is how she would have performed.

“She’s the ultimate boss for that whole region,” one agent said. “You did it in her house, so you better know she’s going to come down hard.”