On a Thursday afternoon, a group of people wait in the library of Mrs. Quennell’s house, where Dr. DuPont (the alias of Jeremiah Pontelli) will hypnotize Grace. Dr. Jordan feels skeptical and expects trickery, yet he also wants to believe. Recognizing his own divided desires, he instructs himself to preserve his objectivity.
Dr. DuPont and Grace enter the room, and Dr. Jordan feels gratified to see that Grace appears unsteady and frightened. Dr. DuPont asks for the light to be turned down, and then he proceeds to guide Grace into a sleep-like state. He instructs Grace to raise her arm and tells her that it has the strength of iron and cannot be bent. He then presses on her arm to demonstrate its unbending strength. Dr. Jordan finds the demonstration too theatrical.
Soon after Dr. DuPont starts asking questions, there’s a loud knocking sound in the room. The sound frightens Lydia, and she clutches Dr. Jordan’s hand tightly. Dr. Jordan feels increasingly like he’s being duped. He also grows physically uncomfortable and has an erotic vision of Mrs. Humphrey. He instructs Dr. DuPont to ask Grace whether she had sexual relations with McDermott. Dr. DuPont does so, and in a voice that doesn’t sound like hers, Grace calls Dr. Jordan a hypocrite for asking. She answers that she would meet McDermott on moonlit nights and let him kiss her and touch her in the same places that she believes Dr. Jordan would like to kiss and touch her. She then claims that she had full control over both McDermott and Mr. Kinnear.
Struggling to keep himself together, Dr. Jordan asks Grace about what happened in the cellar, and she confirms that she was in the cellar and that she helped strangle Nancy to death. She claims that Nancy had to die for her sins, and she celebrates that “this time the gentleman died as well, for once.”
The Governor’s wife cries out Grace’s name in horror, and Grace, still in an unfamiliar voice, responds that she is not Grace and that Grace knew nothing about what she did. Dr. Jordan guesses that the voice belongs to Mary Whitney. The voice confirms his guess, saying that Grace had forgotten to open the window. She felt cold lying on the floor and needed to keep warm, so she borrowed Grace’s “fleshly garment.” Dr. Jordan asks the voice if she’s really Mary. The voice responds with anger that he doesn’t believe her but then trails off. Grace is herself again and says she doesn’t remember what just happened.
Once all the women have left the room, Dr. Dupont confesses that he’s never had an experience like the one they just witnessed. Reverend Verringer says that conventional wisdom would described this as a case of possession. Dr. Jordan, however, insists that it could result from a neurological condition like dédoublement (French for “splitting”), in which a patient might display different personalities that have no knowledge of each other. Dr. DuPont agrees with this theory, but Reverend Verringer objects to it.