This ‘Stranger Things’ Season 5 Theory Says the Broadway Play Spoiled the Ending

Spoilers ahead for “Stranger Things” season five, volume one.

“Stranger Things” fans who saw the TV series’ companion play, “Stranger Things: The First Shadow,” on Broadway or London’s West End may have come away with much more than an extra trip to Hawkins, Indiana — they may have gotten a major clue as to how the series ends.

“Stranger Things: The First Shadow” opened on London’s West End in December 2023 before moving to Broadway in April 2025. Playwright Kate Trefry, who is also a writer on the Netflix series, described the play as the “missing puzzle piece” in the show’s official narrative.

“Stranger Things” creators and showrunners, Matt and Ross Duffer, told The Hollywood Reporter that season five and “The First Shadow” were written concurrently so that “all the mythology lined up.”

“The play starts to tee up some things that are going to be big reveals in season five,” Ross said.

So could the events of the “Stranger Things” play hold the secret to unlocking the season 5 finale? Here’s what to know.

‘Stranger Things: The First Shadow’ is a prequel

“The First Shadow” is set in 1959, about 24 years before the events of season one in 1983, at a time when older characters from the TV show, including Joyce Byers, Jim Hopper, and the late Bob Newby were students at Hawkins High in Indiana.

The play largely focuses on a new student at the school, Henry Creel, whom the “Stranger Things” kids refer to as Vecna.

In season four of the Netflix series, Henry/Vecna is established as the primary villain — a sort of dark wizard residing in the Upside Down who has the ability to command its monsters.

Through a series of flashbacks, it’s revealed that Henry was once a regular human kid with secret magical powers. After the Creels moved to Hawkins in 1959, Henry began using his powers to psychologically torture his family, eventually murdering his mother and sister.

Shortly after, Henry was brought to Hawkins Lab, where he became the first subject in Dr. Martin Brenner’s psychokinetic experiments. Over time, Brenner grew fearful of Henry, so he installed a device in Henry’s neck that tracked and subdued him. He also used Henry’s blood to create more child subjects, including Eleven.

In 1979, a grown-up Henry tricked a young Eleven into removing the device. With his powers restored, he slaughtered most of the scientists, orderlies, and children in the lab. After a brief standoff, Eleven managed to overpower Henry, accidentally opening an inter-dimensional gate and forcing him through it.

In “Stranger Things,” Henry tells Eleven that he sees humans as a “unique type of pest” and resents the structure of everyday life, which motivates him to commit murder. (“Everyone is just waiting. Waiting for it all to be over. All while performing in a silly, terrible play.”)

However, the show does not explain how he came to be this way; instead, it presents him as a natural-born predator, pure evil embodied. By contrast, “The First Shadow” humanizes Henry, creating a richer backstory for the boy who grew up to terrorize Hawkins. It also explains how Henry got his powers in the first place.

That piece of information will likely prove central to the climactic conclusion of “Stranger Things,” as the Hawkins gang aims to rid their town of supernatural terror.

(Warning: This is your last chance to head back if you don’t want spoilers for “The First Shadow” or potential spoilers for the “Stranger Things” season five finale.)

‘The First Shadow’ reveals that Henry was possessed by the Mind Flayer

The stage production opens with a flashback to 1943, when a secret US military mission, known as the Philadelphia Experiment, accidentally sent an entire battleship and its crew to a dark, alternate dimension.

The crew is attacked by a monster, which the “Stranger Things” kids would call a Demogorgon. Only the ship’s captain survives to return to our world — though he’d been infected by the attack, and his blood type had mysteriously changed.

Attempts to replicate the experiment continued in Nevada, using extra-dimensional particles extracted from the captain’s body (who is later revealed as Brenner’s father). But the team of scientists was infiltrated by a Russian spy, who stole a vial of the particles, along with an armful of inter-dimensional tech.

Eventually, the spy’s body was discovered outside a cave near the army base in Nevada — the same cave that an 8-year-old Henry Creel stumbled upon when his family lived in the area.

Henry accidentally activated the technology hidden in the cave, which briefly transported him to the alternate dimension that holds the Mind Flayer, known in “Stranger Things” lore as Dimension X. (This seems to be distinct from the creepy, frozen-in-time version of Hawkins known as the Upside Down, although they’re definitely connected.)

In an interview with Variety, the Duffer Brothers confirmed that the cave in “The First Shadow” is the same one where Max Mayfield is hiding. In volume one of season five, we discover that Max’s consciousness is trapped in a network of Henry’s memories. She picks the cave as a hideout because Henry refuses to follow her in, and she speculates that Henry is terrified of that specific memory.

What does this mean for the ‘Stranger Things’ finale?

The events of the play suggest that Vecna isn’t the real villain of “Stranger Things,” after all.

The Mind Flayer was the main antagonist in “Stranger Things” seasons two and three. When Vecna was introduced in season four, he implied that he was the one who shaped the Mind Flayer and puppeteered its powers. With the backstory from the play, we now know it’s the opposite.

As with Will in “Stranger Things,” the Mind Flayer invaded Henry’s mind and body during his spontaneous trip to Dimension X. When he was transported back to the real world, he carried the power and presence of the Mind Flayer with him.

Throughout the play, high-school-aged Henry struggles against his violent powers, as if it’s not his choice how and when they’re activated. The Mind Flayer, a bodiless entity, seems to speak and act through Henry, using the boy as an avatar to kill small animals. Although Henry tries to resist, each kill makes the Mind Flayer more powerful, and its grip on Henry proves too strong — a grip that likely strengthened after Eleven sent Henry back to Dimension X, where he transformed into Vecna.

If it was the Mind Flayer pulling the strings all along, then defeating the Upside Down’s evils will look very different from what viewers have been led to expect in the final season. Maybe it’ll require severing the connection between the Mind Flayer and its living victims, Henry and Will. Maybe Max can use her knowledge of Henry’s memories to draw out his human side, turning him against his own puppeteer. Or maybe Henry has become too entwined with the Mind Flayer to make it out of this series alive.

Whether the show’s final showdown will be with Vecna, the Mind Flayer, or both, the Duffer Brothers are keeping this information close to their chests — for now.

Volume two of “Stranger Things” season five will be released on Netflix on Christmas Day. The series finale will be released on New Year’s Eve.