"Shop in this place very often?" a man says.
He lures you behind said door …
"Come over here," he says.
And then he whispers: "I'm Secret Santa."
You can't call the cops - they're in on it. And beside, there's no law against making someone's day, CBS News correspondent Steve Hartman reports.
"And this is for you," he says, handing his victim some dollar bills. "Merry Christmas."
"They know they just received something totally unconditional and it was based on nothing more than love - from one human being to another," he told Hartman.
Secret Santa, who wishes to remain secret, will only say that he is a businessman from Kansas City. His plan is to cross the country - going into dozens of thrift stores, laundromats and bus stations, and going up to hundreds of strangers who seem like they could use a Franklin or two.
"I'd like to give you this: $200," Santa says.
By Christmas he'll have given out $75,000 worth of hundred-dollar bills.
"Is this for real?" one man, named Robert Young, asked.
"It's for real, buddy," Santa said.
"And I can keep it?" Young asked.
"It's yours and you can keep it," Santa said.
"God bless you," Young said.
Young is homeless. He was down to his last 20 cents.
Susan Dahl is homeless, too. She was down to her last straw.
"You have use for it?" Santa asked.
"Oh yes, I'm going to go find myself a motel room and get a shower. I've been in the same clothes, people, for 5 days!" Dahl said. "I'm the happiest person in the world right now."
Secret Santa says that joy, that tremendous return on investment - is part of the reason he's doing this.
But here's the bigger reason: Larry Stewart.
Stewart was the original Secret Santa. He kept his identity hidden for 25 years, while giving out more than a million dollars.
Stewart said of his Secret Santa gig: "It warms my heart."
Stewart died last year of esophageal cancer. And on his death bed, a dear friend promised to not let Secret Santa die with him.
"He just squeezed my hand," Secret Santa said. "He didn't say anything."
So, Secret Santa carries on, making perfect smiles on perfect strangers. And like Stewart before, all he ever asks in return is that people do a random act of kindness for someone else someday.
"Can you do that?" he asked one woman.
"You betcha," she said.
"Secret Santa lives in each and everyone of us," Santa said. "It's just a matter of letting him out."