The Dodge Mansion at 2819 P St. NW in the District is shown on Nov. 4. It is owned by Bill Dean, chief executive of M.C. Dean, one of the country’s largest electrical contractors. (Michael E. Miller/TWP)

On the Friday night before Halloween, beyond a front door guarded by bouncers, a few hundred costumed guests drank and danced at one of Georgetown’s most renowned annual parties. Topless models covered in body paint mingled with foreign policy experts and high-powered lawyers as music filled the historic $5 million home known as Dodge Mansion.

At the center of it all stood Bill Dean, the 51-year-old chief executive of M.C. Dean, one of the country’s biggest electrical contractors.

Dean was hosting the Halloween bash for the 11th time. Past parties had featured go-go dancers, fire breathers and props from “Game of Thrones.” This year’s theme was the election. In a toupee and three-piece suit evoking John F. Kennedy on his Inauguration Day, Dean posed for photos with guests in front of a hand-painted backdrop of the Capitol.

“Whether you are for Her or whether you want to make America great again,” the party’s invitation promised, “Dodge Halloween will inspire.”

Instead, inspiration gave way to an allegation of rape and a police investigation.

About 4 a.m. on Oct. 29, after most guests had left, Stephanie Larimore, a model and former Playboy playmate, was on the main floor of the 5,500-square-foot home when she heard cries of distress upstairs, she said.

She hurried her way past a bouncer and followed the noise to a second-floor guest room.

“A girl was lying on the floor, naked, saying she needed clothes and she had been sexually assaulted,” Larimore recalled.

“I was screaming,” the 21-year-old alleged victim said in an interview with The Washington Post.

When Larimore and another woman tried to help her, the attacker allegedly burst into the room, threw the woman against a wall and bashed Larimore’s head on the floor, Larimore said. Larimore called the police. But by the time officers arrived, the man — a friend of Dean’s — was gone.

Police said they are still investigating the incident. Because the alleged assailant has not been charged with a crime, The Washington Post is not naming him. Both he and Dean did not return multiple requests for comment.

Police said Dean is cooperating with the investigation.

Whether there is an arrest, the incident has thrust Dean and his parties into the spotlight. The multimillionaire bachelor — who once compared himself to George Clooney and asked, “Why can’t Washington just have a little bit of freaking fun?” — is now accused of letting things get horribly out of hand.

“These parties,” Larimore said, “should not be happening if there is no control.”

‘A modern-day Gatsby’

Dean has long been among Washington’s wealthiest and most well-connected people. With 1,400 local employees and tens of millions of dollars worth of contracts, M.C. Dean is one of the region’s biggest companies. It is responsible for everything, from maintaining streetlights and trolley-car electrical lines in the capital to the power grid at the Pentagon.

“So much of what M.C. Dean does is behind the scenes: the underpinnings, the infrastructure, lights, signals, the stuff that when it doesn’t work creates real snarls,” said Jim Dinegar, president and chief executive of the Greater Washington Board of Trade. “I’d say the same about Bill. He is a big part of the community but not always out front. He is behind the scenes, playing a pivotal role.”

Dean has been a major campaign donor over the past decade. He and his company have given more than $750,000 to federal, state and District candidates or political action committees, most of which went to Republicans, campaign finance records show. Dean’s company also employed David Catania while he was on the D.C. Council, paying him $240,000 a year. Catania, an independent who ran unsuccessfully for mayor in 2014, did not return requests for comment.

M.C. Dean was founded in 1949 by its namesake, Marion Caleb Dean, Bill’s grandfather. Bill Dean took over the company from his father, Casey Dean, in 1997. He was just 32.

Over the past 20 years, Dean has grown the family business from a traditional electrical contractor with 140 employees to a high-tech global company of 3,500. Its clients range from universities and cities to the U.S. Navy and NATO.

“They are one of the biggest players in the market,” said Mike Eby, editor in chief of trade magazine Electrical Construction & Maintenance. M.C. Dean made $625 million in revenue last year — much of it from federal contracts — ranking it among the top 10 electrical contractors in the country, Eby said. According to its website, M.C. Dean has offices “throughout the Eastern United States, Europe and the Middle East.”

This success has afforded Dean a luxurious lifestyle. He bought Dodge Mansion in 2003 for about $3 million and quickly began hosting lavish Halloween and July Fourth parties. In 2008, he built a 4,145-square-foot second home at Honest Point, Va., overlooking the confluence of the Potomac River and the Chesapeake Bay, shuttling to and from the house in his three-bedroom yacht named Moksha, a Hindu term for spiritual release.

Bill Dean and a guest attend a Haute Living Haute 100 Dinner presented by Dom Pérignon in May 2015 in Miami. (Sergi Alexander/Getty Images for Haute Living)

A year later, Dean bought an even bigger house: the historic, 11,745-square-foot Miami Beach summer home of Kmart founder S.S. Kresge. Dean dropped $8 million on the property, then an additional $32 million on renovations to make it “the ultimate party pad,” according to the Wall Street Journal. The upgrades included a swimming pool, four hot tubs, a Turkish bath, a lawn specially designed for yoga and a pagoda modeled on a Japanese imperial villa. A 12-foot Buddha sculpture was shipped from the District and installed in the house’s nightclub.

Dean renamed the property “Terra Veritatis,” or Land of Truth, in Latin. Nearly 4,000 people attended his birthday party there in 2013, Washingtonian magazine reported.

“He’s a modern-day Gatsby, throwing these big, flamboyant parties,” said Nancy Taylor Bubes, a Georgetown real estate agent. She said Dean often hosted charity dinners at Dodge Mansion and is generally well-liked in the community. Like Gatsby, however, Dean has his detractors.

“I’m a Bill Dean fan,” Bubes said. “But some neighbors can’t believe how these girls dress at these parties. Where there is alcohol and seductive dressing, it’s a real formula for disaster.”

In a private Facebook invitation featuring a picture of JFK in a spacesuit holding Dean’s dog, Shredder, Dean advertised this year’s Dodge Halloween theme as “DC’s own version of Naughty and Nice.” Pumpkins lined the 18 steps leading up to the door of 2819 P St. NW, where guests whose names were on a list received orange wristbands from security guards in black suits. Inside, another security guard blocked access to the upper levels, allowing only Dean’s inner circle, guests said.

On the main floor, voluptuous vampires and sexy SWAT officers rubbed shoulders with Abraham Lincoln and a Confederate soldier. An artist flown in from Miami painted topless models to look like Wonder Woman, an FBI agent, a mermaid and Harley Quinn from the movie “Suicide Squad.”

“Some of his parties have been outrageous,” said David Dunning, a neighbor who said he left before midnight. “This was pretty tame.”

‘The most excruciating pain’

By 4 a.m., only about a dozen guests remained, including the 21-year-old, who is a junior at a university in Maryland. The Post typically does not identify victims of alleged sexual violence.

In a brief interview, the young woman said she had never been to Dodge Mansion before. A friend had been invited, and she wanted to tag along.

After arriving, she proceeded to an upstairs bedroom, where she said partygoers were snorting lines of cocaine. The woman said she sampled a line herself but then went to the bathroom because the drug made her panic.

“This group of girls was there in the bathroom, and I said, ‘My heart, it feels like it’s going to explode,’ ” the woman recalled. “Then I started feeling better after they were talking me through it.”

But then, she said, everything quickly changed with the appearance of Dean’s friend, whom she identified by name to The Post.

“Somehow, [he] got them to leave the room,” the woman said. The two wound up in the connected bedroom, on the bed.

“He locked the door, and he started touching me, and I realized what was going on. I said, ‘Can you stop?’ He wasn’t stopping,” the woman said. He violently bit and grabbed her. “It was the most excruciating pain.” Then he raped her, she said.

When Larimore — a former Miss June 2006 who has been to Dodge Mansion parties — reached her, she was already being comforted by one of the women in body paint.

“She was telling us that she had been attacked, raped, and she was lying on the ground naked, crying,” Larimore recalled.

One witness, who asked not to be named, does not remember the victim saying she had been raped. Instead, she said that she had had sex with the man, but was “uncomfortable” with some of the things he had done to her. She complained she was feeling sick and then began to cry.

After finding her a bathrobe and a bottle of water, the woman in body paint and Larimore were taking her to another room when her alleged attacker intervened.

“He ran toward her to tell her, basically, to shut up,” Larimore said. The man then threw the woman in body paint against the wall before knocking Larimore to the floor, she said. “He stood over me and banged my head into the ground.”

“He grabbed one girl by the hair and threw her across the door and beat the crap out of her,” said the alleged rape victim. “I was standing there frozen.”

After police arrived, at least half a dozen officers fanned out through the house, sequestering witnesses and taking their statements.

“They asked me a bunch of questions, and they reassured me a lot,” the alleged rape victim said.

She did not go to the hospital, she said, because she did not want anyone else touching her body. She just wanted to take a shower and sleep. “I am still in pain,” she said two weeks after the alleged assault.

On Nov. 1, NBC4 aired a segment on the attack at the mansion, citing a police report and showing video of Dean’s house but not mentioning the businessman by name. When her father, who knew she had attended the Halloween party at Dean’s mansion, asked her about the report, his daughter told him she was the victim.

“She said, ‘That was me, Dad,’ ” said the father, a manager at a major bank. “It knocked the wind out of me.”

In an interview near their Maryland home, her parents said they are worried that their daughter is going to stop cooperating with the investigation.

After the party, the woman got a call from a woman who identified herself as a representative of the alleged attacker. Since the call, she has stopped answering questions about the assault despite her parents’ pleas.

“It’s intimidating to deal with someone with such a high profile and aggressive demeanor,” she said of her alleged assailant.

When The Post called the representative, the woman refused to identify herself by name and said: “I can’t comment. I can’t talk about this,” before hanging up.

Larimore said she, too, had received a call from the representative, who asked how she was feeling and what she wanted.

“I don’t want anything from him,” said Larimore, who went to the hospital four days after the attack, was diagnosed with a mild concussion and was still having headaches and blurred vision. “I just don’t want this to happen to any other girls.”

Aaron C. Davis and Jennifer Jenkins contributed to this report.