In a flashback to 1982, Eliot and Thomas Harcourt’s father Ron calls out for his sons while they are out in the woods during a rainstorm. He finds Thomas, who is covered in blood. When Ron asks where the blood is coming from, Thomas apologizes and reasons someone made him do it, prompting Ron to frantically call out for Eliot. In present day, Thomas is being rushed to the hospital by Claire, Jessup and Wes. Claire meets with Dr. Benavidez, who is confused as to what is going on. Seeing Sean, the doctor panics, only to be reassured by Claire he now knows who he is; Claire reveals Sean is her husband.
Speaking with Dr. Benavidez, Jessup tells the doctor to clear the wing, as Thomas is the only one who knows how to get rid of what is there. At the hospital, Claire, Sean, Wes and Lena are rounded up by Frommer’s men while trying to uncover the mystery of how Thomas killed Drill when he was a boy. When Frommer plans to lock up Claire, Sean and Wes, Claire challenges him, telling him he needs them as they are the only ones who know how to end this situation. Frommer gives them 24 hours to solve the crisis.
At Jessup's request, Dr. Benavidez takes him to the children’s ward of the hospital. There, he witnesses a family in grief over bad news about their son. Jessup makes eye contact with the boy’s sister, who is wearing a face mask. Meanwhile, Claire, Wes and Lena go back to Thomas’ basement to investigate, finding information. Their search leads them to a mental institute where they meet Rabbi Ezra, a rabbi who knew Thomas. Meanwhile, at the hospital, Jessup is knocked unconscious by the masked little girl in an elevator. Sean, sensing Drill is there, demands Thomas be moved to an isolated wing and the power shuts off.
When Claire and Wes find a drawing in Thomas’ old room at the mental institute, Rabbi Ezra tells Claire, Wes and Lena about the myth of the “Dybbuk” - an evil spirit which cleaves into your soul and never lets go. Claire comes to the conclusion Thomas killed Drill, who had taken over Eliot. Thomas wasn’t the only one speaking to Drill; Eliot did too. When Thomas refused to send out the signal knowing what would happen if he did, Drill took Eliot’s body. That night in the woods, Thomas actually killed Drill.
A child, under the influence of Drill, however, finds a way to isolate Thomas, keeping Dr. Benavidez and Sean away. Turning on all the lights and bolting the control box, the child makes his way toward Thomas. The child has a question for Thomas from Drill: how did he kill the first one? When Thomas refuses to answer him, the child tells him Drill isn’t going to like that and kills Thomas. In a flashback to 1982, Thomas kills Eliot, knowing Eliot is really Drill. Before it happens, though, Eliot/Drill demands Thomas let him go, grabbing his arm and electrocuting him, leaving a burn mark.
In present day, Dr. Benavidez and Sean try to revive Thomas, but it’s too late: Thomas is dead. Claire, Wes and Lena learn that Thomas’ brother Elliot was inhabited by Drill and that Thomas had killed him in a lightning storm. In the woods, they realize that the only way to kill Drill is after he’s already taken a child. The three agree not to tell Frommer, however, totally unaware they are being recorded by one of his spies. Frommer presents the information to the president, proving one thing: they must kill one child in hopes to save them all.