Theodora is an artist with a sleep disorder, so she decides to participate in the scientific experiment of Dr. Murrow.
The experiment is that Dr. Morrow recruits three patients with sleep disorders and seclude them in a terrifying mansion for several days to analyze their sleep disorders. When Theo arrives at the manor, she arrives the second. The first patient to arrive was Eleanor "Nell".
With her outgoing and cheerful personality, Theo inmediatly befriends Nell (who is attracted by Theo) and confess to Nell that she is bisexual and unsettled, and that she has a boyfriend and a girlfriend at the same time.
Theo proposes Nell to inspect the manor. They both go and feel amazed by the creppiness of the house.
Then the last participant arrives: Luke Sanderson (Owen Wilson) who soon collides with Theo because he thinks she's egocentric and aloof. Then Dr. Marrow and his two research assistants arrive at the manor too.
At night they all have dinner at the main dinning room. There the participants explain their feelings about their slepping dissorders. Theo says she actually likes to have some insomnia since when she is asleep at night is when she gets her best ideas. Luke says he can't stand to have insomnia and that he gets really nervous. Nell says that she has insomnia because her mother was ill since Nell was a kid and that her mother was always complaining at night, so that always kept her away. Even now she suffers insomnia. Theo seems concerned about Nell and she starts to care a lot for her.Wanting to expose his subjects to increasing amounts of terror, Dr. Marrow’s first relates after dinner the story of Hill House. The house was built by Hugh Crain —a 19th-century textile tycoon. Crain built the house for his wife, hoping to populate it with a large family of children; however, all of Crain’s children died during birth. Crain’s wife Renee killed herself before the house was finished and Crain became a recluse. After the story, Marrow's assistant’s face is slashed by a snapped clavichord wire. Theo tries to cure the eye of Marrow's assitant but it seems impossible. The freak accident causes Marrow’s research assistants to leave the manor in search for a doctor.
Then they go to sleep. Trying to sleep, Theo and Nell begin to experience strange phenomena within the house, such as a mysterious force trying to break into their rooms to harm them. Theo cries for help to Nell and the two become terrorized together because of the strange forces trying to enter the room.
Both of them tell this to Dr. Marrow and to Luke that night. But after they are more calmed, they all return to their rooms.
The next morning. That morning Nell continues to hear extrange noises but the others don't believe her. Hugh Crain's wood portrait morphs into a skeletal face and is vandalized with the words "Welcome Home Eleanor" written in blood. Theo and Luke establish their innocence, they confront themselves and then Theo confronts Nell saying she maybe the one who wrote this to catch some attention, but then Theo repents her words and goes to apologise to Nell.
Nell continues to see apparitions, hear strange noises and fins strange objects. So she tries to show Crane's old notebook to Theo in her bedroom but, when she shows Theo the notebook, the pages are empty. So Theo doesn't believe Nell and thinks she's just hardly scared by the creppiness of the manor.
After Nell suffering a serious attack by Crane's spirit at night and being rescued by the others, they all now believe her and they all try to escape from the house.
Trying to convince the obviously mentally-unbalanced Eleanor to leave the house with them, Theo offers to let Nell move in with her, but Nell reveals her relation to Carolyn (she's her great grandmother) and claims she must help the children "pass on". Hugh Crain's spirit seals up the house, trapping them all inside.
A frustrated Luke defaces a portrait of Hugh Crain. Crain's enraged spirit drags Luke to the fireplace where he is decapitated.
Nell is able to lead Crain's spirit towards an iron door. Avenging spirits pull Crain into the door, dragging him down to Hell. Nell is pulled with him, inflicting fatal trauma on her body, but the spirits gently release her on the ground. Her soul rises up to Heaven, accompanied by the ghosts of Crain's victims.
After Nell's death, Theo and Dr. Marrow wait by the gate outside until the Dudleys come in the morning. The Dudleys approach as the sun rises. Mr. Dudley asks Dr. Marrow if he found what he wanted to know, but the traumatized psychiatrist does not give an answer, and neither does Theo. When the gate opens, the two silently walk out and down the road, leaving Hill House behind them
Catherine Zeta-Jones portrays Theo as a cheerful and outgoing (but also somehow egocentric) artist. She close and warm and tremendously easy to deal with. She cares a lot for Nell since she sees her as fragile and shy but also a very good person. Theo even offers Nell to share their house after their stay at the manor. She doesn't mind to confronts the others when she feels they are hurting Nell in anyway. And she felt really sad when Nell dies at the manor.
She in the only survival, alongside Dr. Marrow, of the Hill House. After her experience in Hill House, Theo begins a new renovated life.