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Throughout a large portion of season 5 of *Stranger Things*, the young Holly Wheeler and Max Mayfield find themselves trapped in a realm of memories forged from the past of Vecna. Their mission for a way out in the pivotal sixth episode forces them to experience a life-altering moment from Henry's youth—a discovery that potentially carries the key to defeating him once and for all.

Spoiler Warning: The following details significant events for *Stranger Things* season 5, volume 2.

The Discovery in the Cavern

When she finds Max in the psychic realm called Camazotz, Holly discovers she is hiding out in a chamber that Henry avoids at all costs. A clever observation a spyglass pilfered from Henry's old home allows Holly to realize that the danger lies beyond the cave. Matching her view with the shape, she and Max suddenly fall into a subterranean passage.

There, they witness a young, eight-year-old Henry encounter an wounded, fearful individual. As the boy offers aid, the man fires a gun, wounding the boy in the hand. Fighting for his life, Henry kills the man with a rock. "Was this the turning point?" Holly wonders aloud. The answer is affirmative, but the act went deeper than a fight for life.

Like many elements in volume 2, the truth about the events in the tunnel is detailed in the theatrical production the prequel play.

A Naval Mystery and Secret Science

*The First Shadow* opens with the infamous Philadelphia Experiment, which transported a U.S. Navy ship into a plane known as the Abyss. Demogorgons assaulted it, and the sole survivor was the captain, who came back in a unresponsive state with an altered blood type.

This man's son, a young Martin Brenner, attempted to recreate this experiment in Nevada. One of his scientists pilfered lab samples to give to the Communist spies, who were desperate to launch their own interdimensional projects. That traitor in the tunnel was that very thief.

Unlocking the Mystery

Based on what is known about his research, the case almost certainly contained some of Captain Brenner's infected blood. As shown, Henry is bleeding from his hand. Exposure likely occurred upon handling the contents, which triggered the development of his psychic abilities—traits he would genetically impart to the kids Brenner would experiment on.

A second theory, the box could have held dark matter that was destined to travel to the secret facility, where it acts to anchor the mirror dimension. The prequel shows that the boy was transported in the Abyss, returning 12 hours later as a different person. As a youth, he struggles with the control of a malevolent force, much like how Will Byers was controlled by the Mind Flayer in season 2.

A Weaponized Emotion

His lasting fear of that cave demonstrates how profoundly traumatic the incident was for him. Even as he commands the Hive Mind and works to collapse the Abyss into Hawkins, a fragment of his psyche still exists. Fear is his tool, and the series is building toward a climactic battle between the monster and Will, who has deliberately faced his personal demons to gain strength.

Will's growth has taken a weapon from Vecna. Crucially, Will now knows what Vecna himself fears, and this may grant a critical advantage in the endgame conflict to come.