The Contents of that Briefcase Henry Opens in Stranger Things?
During the bulk of the concluding season of *Stranger Things*, the young Holly Wheeler and Max are held captive in a realm of memories built from the recollections of the villain Henry. Their mission for an escape route in "Escape from Camazotz" leads them to experience a defining event from Henry's youth—a moment that could contain the key to defeating him once and for all.
Heads Up: This discussion contains major spoilers for the second part of the final season.
The Discovery in the Mine Shaft
After locating Max in the world called Camazotz, Holly discovers she is sheltering in a chamber that Henry avoids at all costs. An accidental discovery a spyglass pilfered from Henry's old home helps Holly understand that the true terror lies not within the cave. By aligning her view with the shape, she and Max suddenly fall into a subterranean passage.
They watch a child version of Henry come across an wounded, fearful individual. Attempting assistance, the man fires a gun, hitting him in the hand. In a desperate act of self-defense, Henry strikes the man down with a rock. "Did this make Henry evil?" Holly questions through tears. Essentially, yes, but the act went deeper than a simple act of survival.
In keeping with mysteries in volume 2, the truth about the events in the tunnel is detailed in the live show The First Shadow.
The Philadelphia Experiment and A Spy's Mission
*The First Shadow* opens with the infamous Philadelphia Experiment, which allegedly sent a warship into a plane dubbed the Abyss. The ship was attacked, and the lone returnee was the ship's commander, who came back in a catatonic condition with an altered blood type.
This man's son, a young Martin Brenner, wanted to repeat this phenomenon in remote Nevada. But a disloyal lab worker took experimental components to give to the Soviets, who were keen to start their parallel research. That traitor in the mine shaft is that employee.
The Briefcase's Contents
Based on what is understood of Brenner's work, the container most likely held vials of the altered blood. At that moment, Henry is bleeding from his hand. It's probable he was infected upon opening the case, causing the origin of his telekinetic gifts—traits he would later pass on to the children in Hawkins Lab.
A second theory, the case could have held exotic matter that was destined to travel to the Hawkins lab, where it acts to anchor the parallel world. The stage play explains that young Henry was transported in the Abyss, coming back 12 hours later as a different person. Throughout the play, he struggles with the influence of a malevolent force, much like how Will was controlled by the Mind Flayer in an earlier season.
A Weaponized Emotion
Henry's enduring terror linked to that memory highlights how utterly horrifying the incident was for him. While he controls the collective consciousness and attempts to pull the Abyss into Hawkins, a part of him lingers. Vecna uses fear, and the show is setting up a climactic battle between the monster and Will, who has confronted his own deepest fears to become stronger.
Will's growth has effectively disarmed Vecna. More importantly, Will now is aware of what the monster's own weakness, potentially giving him a key upper hand in the ultimate battle to come.