Stranger Things Series 5 Unveils the Upside Down’s True Nature

For nearly a decade, viewers have puzzled over the origins and purpose of the Upside Down. Now, with the arrival of series 5, the truth is finally out—though, as Dustin Henderson wryly observes, every previous theory has missed the mark. Unless, of course, you happened to catch the stage production, Stranger Things: The First Shadow, which offered its own revelations back in 2023.

The Wall, the Lab, and the Abyss

As the second volume of series 5 opens, Nancy, Jonathan, Steve, and Dustin defy Hopper’s instructions to remain at the church. Instead, they set off to investigate the imposing barrier they encountered within the Upside Down. Dustin, ever the strategist, speculates that the wall is a magical defence conjured by Vecna—a safeguard reminiscent of the Empire’s shield in Return of the Jedi. If his hunch is correct, they might locate the source, disable it, and gain access to Vecna’s stronghold to rescue Holly.

Their search leads them to Hawkins Lab, where Dustin uncovers Dr. Martin Brenner’s archived research. Through these documents, he learns that the Upside Down is not merely a parallel world, but a wormhole—an interdimensional bridge to a mysterious realm they name ‘The Abyss’. This dimension is believed to be the origin of the demogorgons, demobats, and the Mind Flayer, as well as the place where Eleven banished Henry Creel (also known as One) during their confrontation in the Rainbow Room in 1979.

Origins and Motives Revealed

Henry was trapped in this otherworld for four years, until Eleven’s remote contact with a demogorgon created the tunnel that became the Upside Down. Since then, Henry—now Vecna—has exploited this bridge, opening gates in a bid to merge the Abyss with Hawkins and transform Earth into a monstrous domain.

“Netflix wanted us to explain the mythology to them, because we were very adamant early on, 'We don't want to explain it in the show. We like that there's mystery, and that there's a lot that you don't understand by the end of the season,'”

Matt Duffer told Variety.

“They said, 'That's fine, but we would like to know.' I think it was actually a really good exercise – we spent quite a bit of time with our writers figuring out exactly what the Upside Down was. We wrote a 20-page mythology document. It wasn't called the Abyss at that point; it was called Dimension X, which is a Ninja Turtle reference. We've been holding those cards back for so long; it was a real relief to actually be able to show our hands here.”

Stage Show Connections and Hidden Details

Those fortunate enough to have seen The First Shadow will recognise ‘Dimension X’. The play, which delves into Henry’s past, begins in 1943 with the USS Eldridge being drawn into this dimension. The ship’s captain, Brenner’s father, emerges as the only survivor, his crew having fallen victim to sinister, smoky entities.

While the play omits certain connections—such as Joyce and Hopper’s schooldays with Henry, hinted at in the series—it does provide extra context for moments in volume 2. During their journey through Vecna’s Mind Lair, Max and Holly witness a young Henry encountering a bloodied Soviet agent in a mine. The terrified spy wounds Henry, who retaliates fatally and takes a mysterious briefcase. The play clarifies that Henry, missing for twelve days, was found with an injured hand near Nevada’s caves, and the Russian’s body was later discovered there. The briefcase, as revealed on stage, contains secrets about opening rifts to Dimension X and advanced technology.

Unravelling the Mythology

According to the play, the briefcase’s contents transported Henry to Dimension X, where he first met the Mind Flayer. Dr. Brenner later linked Henry to the Mind Flayer after finding his spyglass—now used by Holly in the series—in the caves.

Both volumes of series 5 are now available to stream, with the finale approaching. For those seeking clarity on the latest twists, a detailed breakdown of the ending is available. Which series stands out as your favourite so far?