Beyond this spoiler warning, we reveal what exactly is in the briefcase that a young Henry/Vecna opened in the mines, also known as his worst memory, on Stranger Things 5, Volume 2, and on Stranger Things 5: The Finale. If you don’t wish to know these details from the Stranger Things play, The First Shadow. Head back to the safety of our spoiler-free review of Volume 2.
Stranger Things 5 takes us into the world of Henry/Vecna’s mind prison. Max and Holly are trapped in there, but Vecna/Henry is too, in some fashions. Vecna’s own worst memories also live inside his mind prison, the kind he fears so much he can’t begin to face them. Max and Holly come to understand that the key to escaping the mind prison lies in its inhabitants’ most traumatic memories, and that includes Vecna’s own worst memory. As they search for their escape hatch, they end up making their way through Henry/Vecna’s most traumatic moment. And that journey involves a mysterious briefcase. But what’s inside the briefcase that a young Henry/Vecna opens on Stranger Things 5, Volume 2? The TV series doesn’t answer that question until Stranger Things‘ series finale, which we’ll get to in a minute, but the Stranger Things play, The First Shadow, certainly does. Here’s what it reveals.
There Are Mind Flayer Particles Inside the Briefcase that Henry/Vecna Opens in Stranger Things
In Stranger Things 5, Volume 2, Max drags Holly away before she can see young Henry/Vecna open the mystery briefcase. And that, of course, leads us back to the question of the hour. What’s inside the briefcase that Henry/Vecna opens in the mines in Stranger Things 5? Well, Stranger Things: The First Shadow reveals to us the exact contents of the briefcase. Inside the briefcase that Henry/Vecna opens in his Stranger Things 5 memory are Upside Down particles that the man originally carrying it, a Russian spy, stole from a military base studying the Mind Flayer and Dimension X/the Abyss.
Stranger Things: The First Shadow, the Stranger Things Play, Revealed the Contents of Henry/Vecna’s Briefcase Before the TV Series Did
As we said in our larger piece when discussing what Henry found in the briefcase on Stranger Things 5, “In the Stranger Things play, Dr. Brenner reveals to the audience and a young Henry Creel/Vecna, ‘Your mother tells me that you went missing after your eighth birthday for about…12 hours nearby a military base in Lincoln County, Nevada. You were found outside a cave system with a wound on your left hand. No memory of what happened.’ And later adds, ‘At the military base. That’s where I work, Henry. Where, a few years back, right around your eighth birthday, actually, one of the doctors working with the captain was revealed to be Russian spy. He escaped the facility. The Russian’s body was found two days later in a cave system. Right outside Lincoln County… This doctor had taken something… Something a bored child might be curious about. Something… from beyond our world.’” And something from beyond our world is exactly what Henry/Vecna found when he opened the briefcase we see in Stranger Things 5.
Stranger Things: The First Shadow reveals that when young Henry Creel opened up the briefcase in the mines, he made his first contact with Mind Flayer particles and was thus flayed by the Mind Flayer at this point. The Mind Flayer particles, the Stranger Things play tells us, literally altered his blood and physical composition, transforming him into something other than human. It was this special blood, transformed by the interdimensional contents of the briefcase, that later allowed Brenner to create Eleven and the other children with powers, like Kali/Eight, using Henry’s altered form.
We Finally See What Was in the Briefcase That Henry/Vecna Finds in Stranger Things’ Series Finale
As we predicted, if Max and Holly had stuck around moments longer to see the rest of Vecna’s memory play out on Stranger Things 5, Volume 2, they would have seen black particles rising from the briefcase that Henry/Vecna opens, surging into him as we’ve seen the Mind Flayer do with Will and the other members of the Hive Mind. They would have seen a young Henry Creel become flayed, as he received his powers from the Abyss and began his journey to become Vecna. We know that’s what they would have seen because in Stranger Things 5: The Finale, the series finally reveals to us the contents of the briefcase that Henry/Vecna finds and what happens to him after he opens it.
In the final episode of Stranger Things 5 (and the series), Henry/Vecna finally makes himself face his own worst memory in order to try and capture the kidnapped kids that have escaped him and into it. When Vecna/Henry enters his worst memory, he becomes overwhelmed with it, and we see exactly what happened. As Vecna watches on, young Henry opens the briefcase, and inside is a pulsing red and black stone, a piece of The Abyss or Dimension X. As we watch, black particles rise out of it and seep right into Henry’s open wound, giving him powers.
Henry/Vecna Was Flayed by the Mind Flayer and First Heard Its Voice After Opening the Briefcase
As the black particles seep into a young Henry/Vecna, we flash far away to the Abyss, where the Mind Flayer is waiting for him. “Find me,” its disembodied voice tells Henry/Vecna, setting him off on his journey. As we know, the Mind Flayer particles entering into Henry/Vecna’s wound means that he was officially flayed by the Mind Flayer, and his biological makeup and blood have changed forever… all thanks to opening this briefcase on Stranger Things. This has also given him his powers. In Stranger Things: The Finale, we see the Mind Flayer dance through Henry’s mind as the Russian scientist speaks to him, and then, bam, Henry/Vecna uses his new powers to explode the man’s brain. Oops!
In the End, Vecna Isn’t Sad About What Happened to Him on Stranger Things
Even though Vecna’s worst memory is of finding the briefcase, opening it, and getting flayed by the Mind Flayer, in Stranger Things‘ series finale, he admits that he doesn’t regret what happened. In the end, Vecna reveals that he didn’t have to submit to the Mind Flayer; he wanted to. And the two of them became One, one evil entity. Well, Vecna, good for you, we guess. We hope you like where it led you. We hope that briefcase also feels very proud of itself for causing all this trouble.
Stranger Things 5, Volume 1, Volume 2, and The Finale are now streaming on Netflix.
Originally published on December 26, 2025.
Rotem Rusak is the Editor-in-Chief of Nerdist. She watched The First Shadow on Broadway and can’t believe the Stranger Things play had this much impact on Stranger Things 5.