What's Inside the Briefcase Henry Opens in the Hit Series?

Throughout a large portion of the fifth and final season of *Stranger Things*, the young Holly Wheeler and Max find themselves trapped inside a mental fortress forged from the recollections of Vecna. Their mission for a way out in episode 6 has them witness again a traumatic incident from Henry's youth—a moment that potentially carries the means to overcome him for good.

Spoiler Warning: The following contains major spoilers for the concluding episodes.

A Journey Into the Mine Shaft

When she finds Max in the world called Camazotz, it becomes clear she is hiding out in a grotto that Henry is terrified of. A clever observation a viewing device taken from Henry's old home lets Holly see that the true terror lies outside of the cave. By aligning her view to the cut-out, she and Max tumble into a abandoned tunnel.

In this place, they observe a Henry as a boy come across an man who is hurt and scared. When Henry tries to help, the man fires a gun, striking Henry in the hand. Fighting for his life, Henry ends the threat with a rock. "Is this what corrupted him?" Holly wonders aloud. Essentially, yes, but the event wasn't just a fight for life.

In keeping with mysteries this season, the full story behind the events in the tunnel is detailed in the live show Stranger Things: The First Shadow.

An Interdimensional Incident and Secret Science

The play reveals the 1943 event, which reportedly teleported a vessel into a plane later called the Abyss. The ship was attacked, and the only one to return was the captain, who returned in a unresponsive state with an altered blood type.

The captain's son, a young Martin Brenner, attempted to recreate this experiment in Nevada. But a disloyal lab worker took experimental components to hand over to the Soviets, who were keen to start their version of the tests. That traitor in the mine shaft is that employee.

Unlocking the Mystery

Based on what is known about the doctor's experiments, the briefcase would assuredly have samples of the unique blood type. In the scene, Henry is already bleeding. He likely becomes contaminated upon opening the case, causing the awakening of his powers—powers he would genetically impart to the kids in Hawkins Lab.

Alternatively, the case could have held dark matter that later made its way to Hawkins Laboratory, where it acts to anchor the parallel world. The stage play explains that Henry was transported in the Abyss, reappearing after half a day as a different person. As a youth, he fights the control of a malevolent force, reminiscent of how Will was influenced by the shadow monster in the past.

A Weaponized Emotion

Henry's enduring terror of that cave shows how utterly horrifying the event was for him. While he orchestrates the collective consciousness and attempts to pull the Abyss into Hawkins, a part of him lingers. Vecna uses fear, and the series is building toward a climactic battle between him and Will, who has confronted his personal demons to become stronger.

Will's growth has neutralized a key tactic of Vecna. More importantly, Will now knows what the monster's own weakness, potentially giving him a decisive edge in the endgame conflict that awaits.