The Contents of the Briefcase Henry Opens in the Hit Series?

For much of season 5 of the popular Netflix show, the young Holly Wheeler and Max find themselves trapped in a realm of memories built from the past of Vecna. The search for freedom in the pivotal sixth episode leads them to experience a life-altering moment from Henry's youth—a moment that potentially carries the means to overcome him permanently.

Spoiler Warning: This discussion reveals crucial plot points for the concluding episodes.

The Discovery in the Tunnel

When she finds Max in the mental landscape called Camazotz, Max reveals she is hiding out in a cave that Henry strangely fears. A clever observation a viewing device pilfered from Henry's old home helps Holly understand that the source of fear lies not within the cave. When she lines up her view to the cut-out, she and Max tumble into a abandoned tunnel.

There, they witness a young, eight-year-old Henry encounter an injured and paranoid man. As the boy offers aid, the man panics and shoots, wounding the boy in the hand. To protect himself, Henry kills the man with a rock. "Is this what corrupted him?" Holly asks tearfully. It was a factor, but the event involved more than a simple act of survival.

In keeping with mysteries of the final season, the full story behind the encounter is detailed in the live show Stranger Things: The First Shadow.

An Interdimensional Incident and A Spy's Mission

The play reveals the infamous Philadelphia Experiment, which transported a warship into a plane later called the Abyss. It faced creatures, and the lone returnee was the captain, who returned in a vegetative state with an altered blood type.

That survivor's offspring, Martin Brenner, attempted to recreate this phenomenon in Nevada. But a disloyal lab worker took experimental components to hand over to the Soviets, who were eager to begin their own interdimensional projects. That traitor in the cavern is that employee.

The Briefcase's Contents

Considering what is understood of his research, the case most likely held some of the unique blood type. At that moment, Henry is wounded and bleeding. It's probable he was infected upon handling the contents, which triggered the awakening of his powers—powers he would inadvertently transfer to the kids in Hawkins Lab.

A second theory, the case could have held strange particles that later made its way to the Hawkins lab, where it helps stabilize the Upside Down. *The First Shadow* reveals that Henry somehow wound up in the Abyss, coming back hours later as a different person. Throughout the play, he battles the control of a sinister presence, much like how the character Will was possessed by the entity in the past.

A Weaponized Emotion

The reason Henry avoids the cave associated with the mine highlights how profoundly traumatic the event was for him. While he orchestrates the Hive Mind and works to collapse the Abyss into Hawkins, a part of him lingers. Vecna uses fear, and the series is building toward a climactic battle between Vecna and Will, who has confronted his greatest terrors to gain strength.

This journey has taken a weapon from Vecna. Furthermore, Will now knows what Vecna himself fears, potentially giving him a critical advantage in the series finale that awaits.