What's Inside that Briefcase Henry Unlocks in Stranger Things?
For much of the concluding season of the popular Netflix show, the young Holly Wheeler and Max Mayfield are imprisoned inside a mental fortress forged from the past of Henry Creel. Their mission for freedom in "Escape from Camazotz" leads them to witness again a life-altering moment from Henry's early years—an event that could contain the key to defeating him once and for all.
Heads Up: The following contains major spoilers for the second part of the final season.
A Journey Into the Tunnel
When she finds Max in the mental landscape dubbed Camazotz, it becomes clear she is taking refuge in a chamber that Henry avoids at all costs. A clever observation a telescope taken from Henry's old home helps Holly understand that the danger lies beyond the cave. When she lines up her view through the cap, she and Max plummet into a subterranean passage.
In this place, they observe a young, eight-year-old Henry find an wounded, fearful individual. Attempting assistance, the man panics and shoots, striking Henry in the hand. Fighting for his life, Henry kills the man with a rock. "Is this what corrupted him?" Holly asks tearfully. The answer is affirmative, but the event went deeper than a defensive killing.
Similar to other plot points of the final season, the significance of the events in the tunnel was first explored the live show The First Shadow.
A Naval Mystery and Stolen Research
*The First Shadow* opens with the infamous Philadelphia Experiment, which reportedly teleported a U.S. Navy ship into a plane later called the Abyss. It faced creatures, and the lone returnee was the ship's commander, who came back in a catatonic condition with an entirely new blood.
That survivor's offspring, a young Martin Brenner, sought to replicate this dimensional breach in the Nevada desert. However, a treacherous employee stole research materials to hand over to the Communist spies, who were keen to start their own interdimensional projects. The man in the mine shaft is the one who stole the materials.
The Briefcase's Contents
Considering what is revealed about Brenner's work, the container would assuredly have some of the unique blood type. In the scene, Henry is wounded and bleeding. He likely becomes contaminated upon contact with the blood, which triggered the awakening of his powers—powers he would inadvertently transfer to the kids Brenner would experiment on.
A second theory, the box could have held exotic matter that eventually found its way to the Hawkins lab, where it maintains the stability of the mirror dimension. The stage play explains that Henry somehow wound up in the Abyss, returning 12 hours later as a different person. As a youth, he battles the influence of a malevolent force, much like how Will was possessed by the Mind Flayer in season 2.
The Power of Fear
His lasting fear associated with the mine demonstrates how utterly horrifying the encounter was for him. Even as he orchestrates the Hive Mind and works to collapse the Abyss into Hawkins, a piece of the scared boy remains. Vecna uses fear, and the series is building toward a showdown between Vecna and Will, who has confronted his greatest terrors to become stronger.
This journey has taken a weapon from Vecna. More importantly, Will now is aware of what Vecna himself fears, potentially giving him a critical advantage in the ultimate battle that awaits.