Unraveling the Mystery Behind the Red Room in The Haunting of Hill House

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Warning: This post contains major spoilers for the Netflix original series The Haunting of Hill House, a modern reimagining of Shirley Jackson’s 1959 novel of the same name.

After nine episodes of suspense, the finale of The Haunting of Hill House finally revealed the spine-chilling truth about the so-called Red Room. But the mystery behind the door at the top of the spiral staircase is likely not what you were expecting.

The Red Room was introduced in the show’s first episode during a flashback sequence in which young Shirley (Lulu Wilson) and Nell (Violet McGraw) tried and failed to open the door using a master key given to them by Mr. Dudley (Robert Longstreet). Shirley told Nell that the door had been locked for years, but after they walked away, it was clear there was someone—or something—standing just on the other side of it.

Fast-forward to the opening sequence of the finale, which at first seemed as though it was a repeat of the same scene. But then we get the revelation that it was actually Theo (McKenna Grace), who thought she was in her dance studio, on the other side all along.

An earlier episode also showed the scene from Theo’s perspective.

But the twist wasn’t fully explained until all of the adult Crain siblings, including the ghost of Nell (Victoria Pedretti), were trapped in the Red Room later in the finale.

“We have been in this room, so many times and we didn’t know. All of us,” Nell told her brothers and sisters. “Mom says that a house is like a body and that every house has eyes and bones and skin and a face. This room is like the heart of the house. No, not a heart, a stomach. It was your dance studio, Theo. It was my toy room. It was a reading room for mom, a game room for Steve, a family room for Shirley, a tree house. But it was always the Red Room. It put on different faces so that we’d be still and quiet while it digested. I’m like a small creature swallowed whole by a monster and the monster feels my tiny little movements inside.”

Like Nell, anyone who dies inside Hill House is destined to remain there as a spirit forever. This, in turn, explains why the Dudleys make Hugh (Henry Thomas) promise to never sell or destroy Hill House after Liv (Carla Gugino) poisons their daughter Abigail (Olive Elise Abercrombie) on the Crain’s final night there.

Basically, the Red Room is where the house feeds on the emotions and fears of its potential victims. As Liv tells Nell on the night of their Red Room tea party, “We are the key.”

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Write to Megan McCluskey at megan.mccluskey@time.com