What is Stuart Fails to Save the Universe about? The Big Bang Theory spinoff that ends up crossing over with The Flash

Stuart Bloom breaks a device Sheldon and Leonard built and sets off a multiverse apocalypse. Nine episodes of universe-hopping later, he and his friends get rescued by the Golden Age Flash.

Stuart Fails to Save the Universe premiered on HBO Max on July 23, 2026, the fourth series in the Big Bang Theory franchise after the original, Young Sheldon and Georgie & Mandy's First Marriage. It was created by Chuck Lorre, Zak Penn and Big Bang co-creator Bill Prady. Kevin Sussman stars as Stuart, the owner of the Comic Center, with Lauren Lapkus as Denise, Brian Posehn as geologist Bert Kibbler and John Ross Bowie as physicist Barry Kripke, all reprising their Big Bang roles. HBO Max renewed it for a second season in August.

The premise

Stuart damages a device built by Sheldon Cooper, Leonard Hofstadter and Howard Wolowitz and accidentally triggers what the show calls a multiverse Armageddon. He has to fix it while jumping from universe to universe with Denise, Bert and Kripke, meeting alternate versions of the people they know along the way.

Lorre has described it as a science fiction action- adventure comedy and a deliberate change of pace for him.

"Most of my career has been two people sit on a couch and talk," Lorre said.

Every episode title begins with "Spoiler," and every title delivers. The first is "Spoiler: Gary Dies."

Read more: James Burrows saved a key Two and a Half Men casting, Chuck Lorre says

The universes so far

The jumps get stranger as the season goes:

• The apocalypse — a wasteland where Kripke is a warlord running Caltech as a fortress and Raj has been held prisoner for years.
• The AI state — a world where neural chips shock anyone who isn't calm, and alternate versions of Penny and Zack lead the resistance.
• The magic world — science is a crime, Bert turns out to be a powerful wizard, and an alternate Bernadette is a demon.
• The simulation — Stuart wakes up in a psychiatric hospital under Dr. Amy Farrah Fowler before discovering the whole reality is fake.
• The ruminants — a universe where humanity descended from cows.
• The military world — where the group discovers the soldiers chasing them are their own future selves.

The franchise cameos have included Kunal Nayyar, Kaley Cuoco, Melissa Rauch, Mayim Bialik and Wil Wheaton, plus Christine Baranski, Penn and Teller, "Weird Al" Yankovic and Neil deGrasse Tyson as themselves.

The Flash episode

Episode 8 ends with the group trapped inside a comic book by an entity called the Adversary. Episode 9, "Spoiler: We Couldn't Get Green Lantern," released on September 17, reveals they're in the DC universe, specifically Gotham City, where Mr. Freeze (Eric Allan Kramer) is on the attack. Stuart's plan is to find the Flash and use his Cosmic Treadmill to escape.

They're rescued by Jay Garrick, the Golden Age Flash, played by Andy Ridings, complete with the metal helmet. He takes them home on the treadmill, where they find the Comic Center floating in a void. This is a new version of the character. Grant Gustin, Ezra Miller and John Wesley Shipp are not involved.

The episode title is literal. The writers wanted Green Lantern, but DC said no because HBO's Lanterns was in the works. Penn told Deadline that Lorre was unhappy about it until he and Prady convinced him the Flash fit a multiverse story even better.

Penn on why they picked the Golden Age version: "He's kind of silly."

The writers also leaned on the absurdity of traveling to Central City to recruit a hero against a Batman villain.

The season finale, "Spoiler: Filmed Before a Live Studio Audience," streamed on September 24. Stuart has a second season to keep failing.

Earlier we wrote: Why didn’t Young Sheldon get a Season 8?