In the past, Nell and Shirley try to enter the red room and Theo is shown on the other side of the door in her dance room. 

Adult Steve and Hugh enter the house and Steven sees Luke lying on the floor of the red room and rushes inside. The door shuts behind him leaving Hugh out. 

In the present day, Steven is writing about the night they all went to Hill House to find Luke and talking to a very pregnant Leigh. She eventually begins making fun of Steven and her body begins to deteriorate. Nell appears to Steven and leads him out of the dream. 

Luke, Shirley, and Theo all confront different situations in which Nell leads them out and they awaken in the red room. They all believe Luke to be dead until he comes back after Nell stops him from drinking the tea in his visions of the last time he was in the red room.

Nell appears to all the siblings and explains to them what the red room was to each of them. She is also able to make amends with each of them. 

Hugh wakes up outside the room and speaks with Olivia who refuses to let him enter the red room and rescue the children, for fear of being alone again. He makes a deal with her and she opens the door, so Theo and Shirley can take Luke to the hospital. 

After they're gone, Hugh takes Steven back into Hill House so he can see what went on the night Oliva died. It's revealed that Abigail was the Duddley's daughter and they came looking for her and discovered that Olivia had murdered her. They made a deal with Hugh to preserve the house so they could see the ghost version of Abigail and they would never tell anyone what happened that night so everyone could keep their memories of Olivia alive. 

It is also revealed that adult Hugh sacrificed himself to Olivia and the house so that the children could get out of the room. He then leaves the house to Steven and joins Olivia and Nell in the red room. 

The flashforward shows everyone together celebrating Luke's anniversary of two years sober.