The banking industry is hardly known for its moral rectitude. But if you look beyond the executive suites and venture into compliance departments and operations back offices, you’ll find a handful of sticklers and self-appointed heroes who have made it their mission to save Wall Street from its excesses. Mike is one of them.

As a young banker, he spent his free time volunteering at New York Hospital, feeding Jell-O to burn victims. His mother had worked three different restaurant jobs to support him and his brother, and when he became a father, he figured the best way to honor her was to be there for his four children as much as possible. He coached their football and basketball teams. He also taught adult Bible study and served on the church council at St. Luke’s Lutheran on Long Island. “Mike is not about Mike,” says Charles Froehlich, the former pastor there. “He is about helping others.”

But Mike can sometimes act like the kid who tells the teacher she forgot to assign homework. Take the mooing incident. It was the late ’90s, and Mike was working at Morgan Stanley, where all the trading desks had “squawk boxes”—intercoms that analysts and brokers used to relay information during the trading day. Mike’s problem was that some of the young guys at Morgan Stanley abused their squawk boxing privileges by mooing loudly into them, disrupting colleagues who were trying to get work done. Mike asked his boss to tell everyone to stop, and a meeting was scheduled during market hours. That meant the traders had to call in. And as anyone who has ever met a banker could have predicted, midway through, somebody busted out the gnarliest Mooooooo! in the history of moos. The whole floor went nuts.

“I still get teased about this,” Mike says. “My friend referred to me as the guy who put an end to the mooing.”

HSBC “is the poster child of regulatory infraction—the gift that keeps on giving when I give studies on how not to do things.”

When HSBC called Mike in for an interview in early 2011, he knew almost nobody employed there and had trouble picking up any color about the organization. HSBC wasn’t like Morgan Stanley or Lehman Brothers or any of the other banks where he’d worked. It had $2.5 trillion in total assets, nearly three times more than Goldman Sachs, but the culture was insular, bordering on impenetrable. Most promotions came from within. Some senior managers had even gotten their start as tellers.

After the collapse of the financial industry in 2008, HSBC seemed motivated to lead the industry in scandals. There were accusations of doing business with criminals and rigging markets. In 2010, the year before Mike started, French investigators announced that they had information on 79,000 clients who may have been using HSBC’s private Swiss bank as a way to avoid taxes. (France’s budget ministry reportedly recouped more than $1 billion in penalties.) The same year, U.S. regulators identified “deficiencies” in HSBC’s anti-money-laundering practices, and a Senate report admonished HSBC for letting an Angolan central bank representative attempt $50 million in questionable transfers. HSBC may have even set up offshore accounts for the Angolan rep in the Bahamas.

“It is the poster child of regulatory infraction—the gift that keeps on giving when I give studies on how not to do things,” says Mayra Rodriguez Valladares, a consultant to banks and regulators who has worked with HSBC.

Mike’s role on the sales business management team included pitching new clients and making sure the company hit revenue targets. Still, he was irresistibly drawn to the compliance duties of his job. He saw issues right away—unnecessary bottlenecks, undefined processes and just a general looseness with the rules. In 2011, all major banks, leery of the new Dodd-Frank financial reform package, vowed to make regulatory obedience a top priority. And Mike sincerely believed his bosses would reward him for spotting problems before the feds did. “I thought they could use someone like myself,” he said. He was wrong.

The trading floors at HSBC headquarters in New York are giant, wide-open spaces, rollicking and loud, with hundreds of employees packed in shoulder to shoulder, back to back. You can read your neighbor’s computer screen or hear someone talking to his wife a couple seats down. Privacy is a joke, personal space a luxury best forgotten.

Which is why Mike found it so unsettling, a few weeks into the job, to see Jill crying at her desk. His desk was wedged in between Jill’s and Eileen’s, and at first, he pretended not to notice. But as the days went by, he kept finding Jill breaking down in different parts of the office: whimpering inside glass-walled conference rooms, outright sobbing on the leather couches in the ninth floor lobby.

Mike felt paralyzed. Eileen had previously told him that Jill’s boyfriend beat her and that she was close to being fired for a subsequent dip in performance. “For a while there, I believed Eileen,” Mike said. “I kept [Jill] at arm’s length. I didn’t have a normal relationship with her. I thought she was toxic.”

And so it went until Mike began to detect a pattern. A few times a week, not long after the stock exchange’s closing bell, Eileen would beg Jill to come to Windfall with her. Jill would resist at first, but ultimately relent. Then the next day, Mike said, dozens of people, including senior executives, would crowd around Eileen’s desk as she regaled them with stories that often revolved around Jill’s sexual adventures from the night before. Eileen would try to be low-key when spreading these tales, but Jill sat only a few feet away.

“I would see [Jill] slam the phone and start crying,” Mike remembered. “Sometimes she would say ‘I fucking hate her’ out loud, and Eileen would say, ‘Did she say that to me?’ And then [Jill] would give her the finger. Nobody does that to the boss, especially on Wall Street, and survives.”

In time, it became clear to Mike that Eileen didn’t just want a drinking buddy. He felt she was using Jill as flypaper to attract senior executives and big clients to the bar—and, five years later, when the matter finally landed in court, 900 pages of discovery documents and the testimony of several witnesses helped back up his account.

“Haah … you just like blonds named [Jill],” Eileen wrote to a high-ranking HSBC manager. He replied, “well, i need to admit that she is hot!” Eileen promised to make Jill available when he visited New York the following month. Days before the visit, Eileen had this exchange with him on Sametime, the interoffice chat network [1] Many of the emails and Sametime chats in the piece have spelling or grammatical errors that have not been changed. :

EH [Jill] joining tomorrow Manager good… EH Although should be tonight, she has a cute dress on Manager the dress is not important, goes straight to the floor! ahahahahah EH Your a riot!

In another thread, Eileen asked a co-worker about the previous night: “Do you remember licking [Jill’s] face?” The man wondered if Jill was mad, and Eileen replied, “No, she was laughing about it.”

Mike overheard Eileen on the phone making similar comments. “She would be talking about [Jill], saying she needs a guy like you. After, I would hear Eileen persuading [Jill] to come out for just a few. It was never just a few.”

Gossip about Jill traveled quickly through the open office. One former HSBC staffer, who asked to remain anonymous because she still works in the industry, said, “It was out there in the organization. I don’t think people fully understood how much [Jill] was being impacted.” Sametime chats between Jill and Chris DeLuca, a work friend of hers, reveal a woman being slowly ground down by stares and snickers and half-whispered comments.

JILL I can’t f ing stand it.. I am sitting here in so much PAIN[…] CD is there anything I can do to help you JILL yeah tell [Eileen] to act like a manager

In separate chats with DeLuca, she complained that “just hearing [Eileen’s] voice makes my skin cringe” and “I can honestly say she makes me hate my job, and makes mike and [me] miserable.”

In court documents, both Mike and Jill testified that they believed Eileen derived power from demeaning Jill. Setting up a night out with a pretty young woman helped her build gratitude among clients and executives. It also gave Eileen ammunition if someone crossed her. According to Mike, Eileen repeatedly said that if she got fired, she would dish on everyone in the office: all the affairs, all the lies. He added that she bragged about keeping a running tally of who was having sex with whom.

These threats reflected Eileen’s insecurities within HSBC, where she saw herself as the victim of a sexist double standard. She would occasionally express concern that her partying put a cap on her career prospects. In a March 2012 Sametime chat with a co-worker named Christina Baldwin, she despaired:

EH I don’t even like myself and what i’ve become CB don’t say that. you r doing great… the people around you have changed. EH it seems like their behavior is what is getting them ahead though… and behavior I had years ago holds me back.

Jill is bound by a confidentiality agreement and did not respond to interview requests for this story. But she corroborated much of Eileen’s conduct in a deposition for a federal trial. “I often felt she would try to offer me up to clients sexually, both internally and externally,” Jill said. “She would often make comments about me or lies about me and share them with other employees. One time I had a suitcase for a trip and she pulled out a pair of shoes and in front of all my colleagues said, ‘Look, aren’t these’—I think she used the word—‘fuck-me shoes.’”

Jill also alleged inappropriate touching, saying that Eileen once attempted to pull down her blouse around other employees. In another incident, at Windfall, Jill said Eileen “grabbed my buttock.” (Mike was there, too, and says the force of Eileen’s butt smack was so great that Jill was briefly lifted off the ground.)

Much of Jill’s testimony focused on an HSBC-sponsored conference in Key Largo, Florida, that turned into an old-fashioned Wall Street bacchanal. Jill said she was harassed by several HSBC executives, including one senior manager who talked about “eating out my ass. He described how he just wanted to—and I think these are his words, not mine—‘get up in there’ at this particular event.”

Jill described spending some of that same night in Key Largo fending off the advances of Eduardo Legorreta, the head of global market sales with HSBC Mexico. “He put his hand on my leg, trying to put it up my dress, and I hit him away. Throughout that evening [Eileen] was encouraging this type of behavior,” Jill testified. At one point, she said, Eileen physically pushed her toward Legorreta. Jill’s Sametime chats shortly after the incident tell the same story:

Jill I was running away from Eduardo Legorreta – he grabbed my a$$.. that is when I was like WE HAVE TO GO! … I was getting a little annoyed w Eileen bc she kept pushing leggo on me – im like never going to happen! Stop instigating him

And yet, she, too, felt paralyzed when it came to Eileen. At one point, she told DeLuca that she’d “fucking had it” and was “done w her” and that she’d tell human resources “everything.” She never did.

“Try and get out of there at a decent hour. No Eileens 2nite,” DeLuca wrote to Jill during one bad patch. “Thanks—yeah no def not any eileen’s,” Jill responded. But in this case, as in so many others, she quickly found herself back at Windfall, drinking late into the night and then being run through the rumor mill in the morning.