In March of 2022, Mark Herman, a dog walker and recreational drug enthusiast in Upper Manhattan, came into possession of a dog, a painting and a story.

The dog was Phillipe, a 17-year-old toy poodle that belonged to Mr. Herman’s only client, an 87-year-old retired law professor named Isidore Silver.

The painting, which belonged to Mr. Silver, may be a lost work by the artist Chuck Close, whose canvases once sold for as much as $4.8 million. Or it may not.

Therein lies the story. On a recent afternoon in his cluttered apartment, Mr. Herman offered a broken chair and began a circuitous account of friendship, loss and a commercial art market not meant for people like him.

In 1967, Chuck Close was an instructor at the University of Massachusetts Amherst, “desperately unhappy” and eager for the New York art world, when the school offered him his first solo exhibition, in the student union. Mr. Close, best known for his monumental photorealist portraits, had not yet found his style and was painting in an expressionist mode heavily influenced by Willem de Kooning.

For his exhibition he chose 31 works, several of which featured male and female nudity. One painting depicted a semi-abstract Bob Dylan wearing only a T-shirt. Others had titles like, “I’m only 12 and already my mother’s lover wants me” and “I am the only virgin in my school.”

There were complaints. One drawing was stolen.

The university removed the paintings. Mr. Close sued on free speech grounds. His lawyer, in what became a well-known First Amendment case, argued that “art is as fully protected by the Constitution as political or social speech.”

The lawyer was Mr. Silver, future poodle owner.

Mr. Silver prevailed in court, then lost on appeal. Mr. Close, who later dismissed the exhibition as “sort of transitional work,” lost his job.

The paintings, which were returned to Mr. Close, disappeared from the record.

Both men moved to New York. Mr. Close became one of the pre-eminent artists in America, even after paralyzing spinal trauma, until several women accused him of sexual harassment in 2017. Mr. Silver, who never liked practicing law, joined the faculty at John Jay College of Criminal Justice. In his bedroom closet in Upper Manhattan, he kept a large rolled up painting that for half a century he never showed to anyone. The painter, he claimed, was Chuck Close.

Enter the dog walker.

Mark Herman, who was almost two decades younger than Mr. Silver, had studied the Buchla synthesizer and television production at N.Y.U., worked in a photo lab, run a recording studio and sold high-end stereo equipment online. By the time the two men met six years ago, he was walking dogs to support himself.

The older man was, to put it gently, a volatile character. “He had his moods,” Mr. Herman, 67, said, adding: “I know how to deal with people like that. You say yes.”

He and Mr. Silver hit it off, Mr. Herman said. Both liked movies and Lenny Bruce, and both loved Phillipe, whom Mr. Herman called Philly-bones. Mr. Herman started lingering in Mr. Silver’s apartment after his morning walks, staying for coffee and cake. Mr. Herman made his own cannabis oils, and he gave some to Mr. Silver for his back pain.

When the pandemic hit, and Mr. Herman stopped walking dogs, the two men talked for hours on the telephone daily, Mr. Herman said. Mr. Silver had alienated most of the people close to him, but he formed a bond with Mr. Herman.

“He had a temper,” Mr. Herman said. “If he wanted to say something, you stand back and take it. That’s the way I dealt with him, because he was very explosive.”

Asked what would set his friend off, Mr. Herman replied: “Everything.”

Still, Mr. Herman said: “He was like a second father to me. I loved that guy.”

One day Mr. Silver mentioned having represented Chuck Close in the 1960s. Mr. Herman was intrigued. He had seen an exhibition of Mr. Close’s portraits at the Whitney Museum of American Art in 1981 and had loved it. “I was blown away to see that in person,” he said.

In September 2021, Mr. Silver wrote about the case in The Daily News, asking, “What happened to the paintings at the exhibition?” before answering, teasingly, “Memory almost totally fails.” (Mr. Close died in August 2021.)

Mr. Silver’s health declined. Mr. Herman on three occasions arrived to get Phillipe and found Mr. Silver on the floor. Twice he had to call 911.

Mr. Silver told Mr. Herman about the painting rolled up in the closet. The plastic around the canvas was almost black from Mr. Silver’s pipe smoke. “He basically said, ‘Take the painting,’” Mr. Herman said. Mr. Herman did.

“Not only did I get the painting, but I got Phillipe,” he added. “I just took him.”

Mr. Silver died last March. Phillipe died in September. Mr. Silver did not include Mr. Herman in his will, but the family gave him $5,000. And he had the painting.

Mr. Herman, who had stopped walking dogs and was living on Social Security, checked out the auction prices for Mr. Close’s work: $3.2 million for a portrait of Philip Glass; $4.8 million for a portrait of the painter John Roy. Even a very early abstract painting, “The Ballerina,” from 1962, sold for $40,000 at Sotheby’s, more than double the auction house’s estimate.

Under the influence of magic mushrooms, Mr. Herman received some numbers: first $1.4 million, and later $10 million. “But they’re pranksters,” he said of the mushrooms. “I would not jump out of an airplane and say, ‘Oh, the shrooms packed my chute.’ I wouldn’t trust them that far. They don’t know everything.”

Still, maybe Mr. Herman’s ship had come in.

“If I lived in a mansion, I’d keep it,” he said. “I wanted to sell it.”

An old prep school friend who had become part of the art squat movement in France warned him against hanging onto it. “He said the art world is the most cutthroat of any, even worse than Hollywood,” Mr. Herman said. “He was saying there might even be people coming in the middle of the night to steal it from you. I said, What?!” Mr. Herman said he was afraid to unroll the painting, lest he damage it.

Through an internet search, he found Pace Gallery, Mr. Close’s longtime dealer. “Pace wanted $5,000 for stretching and evaluation,” Mr. Herman said. He did not have that kind of money.

He went to Sotheby’s auction house, which offered to put it up for sale in December 2022, with an estimate of $15,000 to $20,000 — low because it was an early work, and because Mr. Close’s market had softened since the accusations of sexual harassment. The cost of stretching would come out of the sale price.

When the auction house unrolled the painting, it was the first time Mr. Herman had ever seen it, along with the signature: “Close 1965-6.” The colors were vibrant; the textures densely layered. “Almost like de Kooning,” Mr. Herman said.

But here things take a turn.

The auction house had contacted Pace Gallery, which had contacted Mr. Close’s studio. Neither had any record of the painting. “While this doesn’t necessarily mean that the work is not by Chuck Close, it is certainly a red flag for both us and Pace,” an associate specialist at Sotheby’s wrote to Mr. Herman. There would be no sale. In subsequent messages, she advised Mr. Herman that he would receive an invoice for $1,742 for stretching the canvas, and that he should remove it soon or face storage fees.

Sotheby’s declined interview requests for this article; Pace Gallery responded only with a terse statement: “We’ve looked into this further and Pace does not have any information on the below work, or the 1967 exhibition.”

Mr. Herman’s big windfall had not materialized. Maybe he had a painting by one of America’s great artists. But he was in the wrong art market at the wrong time.

In recent decades, as prices for paintings have skyrocketed, so has litigation around their authenticity. In response, artists’ studios and estates have moved away from authenticating stray works that pop up, in order to avoid being sued. The estates of Andy Warhol, Jean-Michel Basquiat, Jackson Pollock, Keith Haring and Roy Lichtenstein, among others, all closed their authentication services. At least one authenticator had his life threatened for not approving a painting.

Authentication is especially difficult with early work, said Tom Eccles, who runs the Center for Curatorial Studies at Bard College.

“It’s almost impossible to authenticate an early work — they didn’t document the work, they didn’t photograph the work, it’s probably not in a database,” Mr. Eccles said. “So it’s not to say these works aren’t real, but it’s very hard to authenticate them.”

Often, as with Mr. Herman’s canvas, early efforts do not reflect the artist’s mature style, Mr. Eccles said, so they cannot be authenticated by analyzing the technique or materials. “And even if one does authenticate them, are they worth a lot of money? Probably not.”

Mr. Herman tried other auction houses and museums, including the Museum of Modern Art and the Whitney. No interest. He contacted the nonprofit International Foundation for Art Research, which authenticates work, but it wanted $3,000, plus information regarding the painting’s provenance and expert opinions about the work — all things that Mr. Herman did not have.

He wrote to the University of Massachusetts Amherst to see if it had records of Mr. Close’s 1967 exhibition. Another dead end.

Finally, on July 13, he and a friend rented a van to retrieve the painting from Sotheby’s. It was his second trip to the auction house, this time without the great expectations of the first. And now he was out $125 for the van and worried that Sotheby’s would not let him take his painting unless he wrote a hefty check for the stretching. “I was excited the first time, but now it’s like getting a colonoscopy,” he said on the sidewalk outside.

The painting, stretched on a frame, was even more radiant than it had looked when the auction house first unrolled it. It bothered Mr. Herman that Pace had not looked at the actual painting, just dismissed it based on a photograph. The stretched canvas was almost six feet tall. It just barely fit into the van.

Back at Mr. Herman’s apartment in Washington Heights, it dominated the living room. Mr. Herman looked exhausted. He had been living with disappointments since December, to say nothing of his life before then. He missed his talks with Mr. Silver. “It’s documented that he was the lawyer at Chuck Close’s trial,” he said, frustrated. “And there’s the unbroken chain of custody in his closet.”

He looked at the painting. You couldn’t not look at it.

“I’m enjoying it right now,” he said, “but you don’t want to have ice cream for breakfast, lunch and dinner.” Besides, his apartment, which he shared with his daughter-in-law and his grandson, was no place for a painting like that. “It wants to bust out and be alive,” he said. “It wants to be out in the world. It’s crying out for a home in the Hamptons.”

At last, he caught a break. On July 17, four days after Mr. Herman’s van run to Sotheby’s, an archivist at the University of Massachusetts uncovered a file on Charles Close’s 1967 exhibition, including an issue of the school newspaper dedicated to the controversy. There on Page 3 was a photograph of Mr. Herman’s painting.

“Proof indeed,” said Mr. Eccles, the curatorial authority from Bard. “What a story!”

A spokesman for Sotheby’s, shown an image of the newspaper, said the auction house did not authenticate works and declined to comment. Pace reiterated that it had no details on the painting or the exhibition.

Mr. Herman was already making plans. With the sale of the painting, he could move out of his apartment and get a place for himself and his girlfriend.

“I’m on the moon,” he said. “I’ve enjoyed living with it. But I want to get it out of here, because a knife could fall on it. A can of paint could spill on it.”

What was it worth? He truly did not know. But after so many disappointments with the painting, what did he have to lose?

“There’s got to be some money in it,” he said. “Don’t you think?”

Audio produced by Jack D’Isidoro.