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If there is a god of ludicrous ideas that later seem inspired, he must have smiled on Brian Thompson one night four years ago. A comedy writer living in Los Angeles, Thompson had been bingeing on true crime podcasts when he decided to create a show that would plumb the stupidest, least consequential mystery he could imagine.

For reasons he can't fully explain, he came up with: Whatever happened to pizza at McDonald's?

Maybe you are too young to remember. Perhaps you forgot. Or there's a chance you've blocked it. But the home of the Big Mac began selling pizza in the mid-1980s.

McDonald's gave up a few years later. Nobody lamented the passing of McPizza, and nobody was urging its return. Which, to Thompson in the fall of 2016, made the topic all the more appealing.

"I knew there were a lot of McDonald's that are open 24 hours, so I could call one of them right then," he said. He called two. At the first, an employee hung up. But at the second, a manager was sincerely stumped. "Sorry about that," he said, politely. "Have a good night."

By 3 a.m., Thompson had edited the calls and added some narration. Then he uploaded Episode 1 of the "Whatever Happened to Pizza at McDonald's?" podcast to iTunes. That was 177 episodes ago.

More than just a joke

What started as a lark meant to amuse himself has evolved into something far richer — a deadpan satire about podcasts, the business of podcasting and the quirks of investigative journalism.

"Whatever" has a core audience of about 30,000 listeners. It has spun off an online version of a board game and a self-published book ("How to Be an Investigative Journalist"), and Thompson has shot a TV pilot episode that his manager is shopping around Hollywood.

While attempting to unravel the "mystery" of McPizza, Thompson has turned doggedness into a kind of performance art. He has traveled to a remote Alaskan island to study an abandoned McDonald's and walked up to the gate of the White House, where he tried to enlist the help of President Donald Trump.

One trick to keeping this enterprise alive and entertaining is Thompson's refusal to accept answers to the show's titular question. McPizza failed for reasons that should have seemed evident before it was rolled out: It's way off brand, and it didn't bake fast enough to keep pace with the rest of the menu.

Thompson won't accept any of that. On the podcast, he plays a character — also named Brian Thompson — who regards himself as an intrepid seeker of truth and seems to think he's digging into a riddle for the ages.

"My character has always refused to believe reality," Thompson said. "And that kind of opened up the possibility that the show could be anything I want." Plus, the company has never returned one of his calls, leaving him free to cook up his conspiratorial theories.

He takes pains not to belittle the restaurant workers, who have no choice but to treat the oddball on the phone diplomatically. He makes himself the butt of every joke. "I don't want this to be a prank show," he said. "I really want to be the dumbest person in the room at all times."