Stranger Things Spinoff Will Answer What’s Inside the Briefcase and Other ‘Loose Threads’ From the Season 5 Finale, Duffer Brothers Promise

If you’re all caught up on Stranger Things, you’ll be aware of a plot thread left dangling in the Season 5 finale that has to do with a briefcase. It turns out this will be addressed in a live-action Stranger Things spinoff — although there’s no word when.

Warning! Spoilers for Stranger Things Season 5 Episode 8, The Rightside Up, follow:

In the Season 5 finale, we see Henry Creel / Vecna finally face his greatest fear: the traumatic memory of the day he was infected by the Mind Flayer and gained his powers. In this scene set inside Henry’s mind, we finally find out what was inside the briefcase that child Henry opens after bludgeoning its previous owner, an unnamed scientist, to death. Inside is a mysterious rock, which glows with an unknown energy before fusing with Henry. This, we understand, is how Henry became one with the Mind Flayer, and sets in motion all the events of Stranger Things that followed.

But what was this rock exactly, and how did it come to be in our world in the first place? An article on Netflix confirms the rock contains Mind Flayer particles, which then possess Henry. “Come find me,” the Mind Flayer beckons. And the dying scientist warns: “It will consume you.”

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In a subsequent interview with Variety, Stranger Things co-creators Matt and Ross Duffer teased that the planned spinoff will explain all — and answer other plot threads left dangling.

“The spinoff is going to delve into that and explain that, and you’re going to understand it,” Matt Duffer said of the briefcase rock. “But it’s a completely different mythology. So it’s not a deep exploration of the Mind Flayer or anything like that. It’s very fresh and very new, but yes, it will answer some of the loose threads that are remaining.”

Stranger Things: The First Shadow Gallery

The briefcase scene is explained in vague terms by Stranger Things: The First Shadow, the canon play that acts as a prequel to the events of the Netflix show. We’ve run through the plot of the play already, but in summary, it confirms that Henry and the scientist are transported to what was then known as Dimension X. When Henry returns, he is much changed, and Dr. Brenner (Matthew Modine) eventually uses him as part of his experiments in Hawkins National Laboratory.

But even before then, the play tells us of a 1943 United States experiment to turn submarines invisible during World War 2. As part of this, they travel to Dimension X. Perhaps that’s where the mysterious rock originally came from, and how it ended up in our world in the first place.

Either way, we will get an answer to the briefcase rock in the spinoff show, although we’re very light on the details. The Duffer brothers are working on it as we speak, and described it as a “clean slate.”

“Completely new characters, new town, new world, new mythology,” Matt Duffer said, adding: “No common characters.”

If the spinoff is going to explain the briefcase rock, it seems likely it will in part be set in the 1950s. But other than that, it’s anyone’s guess. Netflix actually has two announced Stranger Things spinoffs in development, the first of which is Stranger Things: Tales From ’85, a new animated series due out at some point this year. This is set in the same universe between Seasons 2 and 3, and follows the original characters as they “fight new monsters and unravel a paranormal mystery terrorizing their town.” The second spinoff, which the Duffer brothers are referring to above, is an unnamed live-action series.

We’ve got plenty more on Stranger Things, including the Duffer brothers explaining the ambiguity of Eleven’s ending.

Image credit: Netflix.

Wesley is Director, News at IGN. Find him on Twitter at @wyp100. You can reach Wesley at wesley_yinpoole@ign.com or confidentially at wyp100@proton.me.