There are a million stories in the daily life of a city, and some of them — too many of them — validate the misanthrope’s hateful view of mankind and confirm the realist’s lack of faith in human decency. This story, about a wretched, little crime against a senior citizen, might do all that.

But then, you might be as surprised by the turn of events as Bob Padousis was.

Let’s make that Dr. Padousis, if you please, because he is a retired dentist, 78 years old, and a Vietnam War veteran who was stationed in Cam Ranh Bay with the U.S. Army Dental Corps in the 1960s.

These days, Dr. Padousis lives with his wife in Essex. He has a disability for which he relies on a walker — and the help of a caregiver when he needs to go somewhere.

A couple of Wednesdays ago, Dr. Padousis had an appointment at the VA Medical Center in downtown Baltimore.

Afterward, he and his caregiver, Gladys Jackson, decided to visit Lexington Market a few blocks away. “I hadn’t been there in 20 years,” Dr. Padousis says.

They had lunch at Faidley’s Seafood — always a good choice — on the Paca Street side of the market. Then, around 2 p.m., they walked through the main hall toward Eutaw Street. When they reached the glass doors, Jackson held one of them open. As he walked through, Dr. Padousis tripped and fell. He thinks he caught his foot on a rubber mat.

“I landed in a prone position, on my stomach, face down,” he says. “It happened so fast. My wallet was in my jacket pocket on the left side, and it must have been visible after I fell.”

In the next instant, someone grabbed the wallet and pulled it away.

“He’s stealing my wallet!” Dr. Padousis yelled.

The thief — described as a man in his 40s, with eyeglasses, a gold-plated incisor, wearing a cap, tan pants and a gray jacket — started to run south on crowded Eutaw Street.

Some witnesses pointed at him and called for help: “He just took that man’s wallet!”

But others yelled encouragement to the thief: “You got it! Go ahead. You’re good. Go!”

Chris Roberson heard all this, sized it up quickly and decided to get involved.

He’s 38 years old, a nurse practitioner at the Institute for Human Virology on the University of Maryland School of Medicine campus a few blocks south of the market. He works with patients with HIV infections.

Roberson had just come from lunch when he heard the commotion and saw an old man on the ground and a younger man running away. Roberson, dressed in blue jeans and a polo shirt, his UM identification tag dangling about his neck, decided to follow the thief.

“He was jogging, not too fast, and I saw him cut into the alley across from the market,” Roberson says. “I figured he would not want to be too conspicuous, you know? So I predicted he would cut through the alley and pop up on Fayette Street. So I went to Fayette and saw him pop up in the crowd. I heard police sirens.”

Roberson thought he could track the robber and help the police locate him.

But after following the guy for a couple of blocks, Roberson decided to escalate his effort. Near a fast-food restaurant at the corner of Fayette and Howard streets, he got in front of the guy. Got in his grill.

“Did you really take that older gentleman’s wallet?” Roberson asked.

“No, I didn’t,” the guy in the cap said.

Roberson could see the wallet tucked in a stack of papers under the guy’s left armpit.

“I don’t have no wallet,” the guy in the cap insisted.

“The one right under your armpit?” Roberson said. “You’re going to give me that wallet right now or I’m gonna ...”

And, just like that, the robber, hearing the police sirens, handed the wallet to Roberson and jogged off toward Park Avenue.

Roberson hustled back to Lexington Market, where he found the elderly man who’d been robbed resting against his walker, his caregiver at his side.

“Here you are, sir,” Roberson said.

“Is this my wallet?” Dr. Padousis looked up and asked.

“Yes,” said Roberson. “I encountered the gentleman who took it from you and got it back from him.”

“I can’t believe it,” Dr. Padousis said.

He offered the younger man a cash reward. But Roberson declined it.

Dr. Padousis spoke of having visited Lexington Market since boyhood. But here was his first visit in 20 years: He fell, and some lowlife picked his pocket while he was down.

“That shouldn’t have happened to you,” Roberson said. “I hope it won’t deter you from future visits.”

Dr. Padousis tried to offer him a reward again, but Roberson declined again. “Try to enjoy the rest of your day,” he said, then walked back to work.