Who Is Mr. Whatsit? The Stranger Things Season 5 Twist Explained

Contains spoilers for "Stranger Things" Season 5 Episodes 1 & 2 — "The Crawl" and "The Vanishing of ..."

In the world of "Stranger Things," nobody is ever safe. That means that in the fifth and final season of the Duffer Brothers' hit Netflix series, Holly Wheeler, a constant throughout the series who's now played as a preteen by Nell Fisher, finds herself in danger thanks to her strange "imaginary friend" Mr. Whatsit.

Holly, who's the younger sister of series protagonists Mike and Nancy Wheeler (Finn Wolfhard and Natalia Dyer, who have appeared on the show since its inception) and daughter of Karen and Ted Wheeler (Cara Buono and Joe Chrest), was played in previous seasons of by twins Anniston and Tinsley Price. Now, in Fisher's hands, Holly gets a much more central role, starting in the very first episode of season 5 of "Stranger Things," titled "The Crawl." No longer a background player in her brother and sister's story, Holly is reintroduced reading "A Wrinkle in Time" by Madeleine L'Engle — a beloved science fiction book that could hold clues to the season's eventual conclusion — and she won't stop talking about Mr. Whatsit.

The problem? Mr. Whatsit isn't really "imaginary," per se; we see him just out of frame, and there's clearly something much more frightening going on with this shadowy character. If you've seen "Stranger Things" before, you know this show tends to split its time between the troubled and fictional town of Hawkins, Indiana and the sinister, supernatural "Upside Down" that lies below ... so is Mr. Whatsit a creature from the Upside Down? Yes, he is. He's Henry Creel, also known as Vecna, the series' Big Bad played by Jamie Campbell Bower.

As we catch up with Holly's older siblings, we also learn that Holly is in trouble at school — to the point where Karen has to go and speak to her teachers — because of her troubling connection to and with this "imaginary friend" Mr. Whatsit. (As far as the teacher is concerned, Holly was standing at a fence near the edge of the school talking to nobody in particular; from Holly's perspective, she was just chatting with her close personal buddy Mr. Whatsit.) After Karen speaks to Holly's teachers, Mike and Holly take a moment to bond, with Mike sharing his prowess in "Dungeons & Dragons" (the eternally popular tabletop role-playing game) and creating a character "for" Holly, presumably for her to adopt when she's a little older. Interestingly, Mike decides that Holly would play the game best as a cleric; among other things, clerics in the game can open previously closed doorways and pathways.

After her terrible day at school, Holly cries alone in her room while her parents argue over her recent issues with this bizarre Mr. Whatsit. That's when the worst possible thing happens, at least in "Stranger Things" terms — a Demogorgon, perhaps the most famous monster found in the Upside Down, appears in her bedroom. As "The Crawl" ends and "The Vanishing of ..." begins, we learn Holly's fate, and it doesn't look good.

"The Vanishing of Holly Wheeler" starts with a bang as the Demogorgon attacks poor Holly in her room at the Wheeler house ... and unsurprisingly, both Ted and Karen show up to see what the heck is going on with their youngest child. As the Demogorgon keeps trying to get at Holly, who frantically attempts to escape its clutches, she and Karen hide in the full bathtub — somehow, the water keeps them safe, albeit briefly — but their bubble bursts when Ted tries to help and is immediately thrown into a wall by the Demogorgon, leaving him with horrible injuries. 

Despite Karen's best efforts to protect her young daughter, the Demogorgon wins out. By the time Nancy and Eleven (Millie Bobby Brown) get to the Wheeler house, it's far too late; Holly is nowhere to be found, and Karen is close to death. Thankfully, the two girls rush Karen to the hospital before she can succumb to her injuries, at which point they, along with Mike and the rest of the gang, realize that Holly has been taken by portal to the Upside Down.

Eleven heads to the Upside Down to find Holly, but then we see a vision that clears everything up (experienced, as it turns out, by Noah Schnapp's Will Byers). As Mr. Whatsit leads Holly to the brightly lit Creel house (which is also frequently depicted in horrifying disarray in the Upside Down itself), Mike and Nancy get their mother to write down what Holly claimed Mr. Whatsit's name is ... and it's Henry, the original name of Vecna.

We'll find out what happens to Holly across the rest of Season 5 of "Stranger Things," which drops three more episodes on Christmas Day and the finale on New Year's Eve.