• WARNING: Spoilers



    -NOTE: In the Italian version all actors are listed by their real Italian names. In the US version they are listed by more American-sounding names. Below they are listed by their real Italian names.**

    Muriel Hampton Arrowsmith (Barbara Steele) has entered the lab of her husband Dr. Stephen Arrowsmith (Paul Muller) with a drink. He chastises her for entering without permission, commenting on her drinking. She acknowledges that he is leaving for a scientific conference where he will be with other fanatical good-for-nothings like yourself she taunts. He tells her not to speak to him like that. She reminds him that she is his wife and would like to spend the night with him. They kiss. Muriel notices that this has been observed by Solange (Helga Liné), who is waiting to see him off on his long journey. They say their goodbyes and he tells her he will only be a couple of days gone. The carriage is brought up by David (Rik Battaglia) who asks about the new plants. He is told to water them in the greenhouse. Dr. Arrowsmith leaves.

    Muriel goes to the piano and plays music. Hearing this, David drops what he is doing and heads into the house to meet her. Muriel disrobes, puts on her nightgown and perfume and begins passionate kissing with David, which progresses to the bed. She stops, suggesting they are too near Solanges room and they should go to the greenhouse. Once there, they lie down and begin passionate kissing.

    Outside we see Dr. Arrowsmith waiting and watching for a signal from Solange. From an upstairs window we see a light flashing back and forth. Holding his cane, he enters the greenhouse and confronts the lovers. He strikes David in the face with his cane, then his wife. Next we see both of them strung up on a wall with Stephen whipping them. He uses a heated poker on David. Next we see Stephen pouring a glass of water from a pitcher. Both look thirsty and Muriel begs for a sip. He brings it close, then pours it out. She curses him with her hatred, but then confesses that she recently remade her will, leaving all her wealth to her step-sister Jenny.

    Stephen is pouring through a book, presumably a law book, as he plans what he will do. Solange tells him he will have to keep her alive, but that Solange wants her share of the money that he has promised her. He reassures her that he will win and Solange will get what is coming to her. Then he says Jenny will inherit the money, but everyone knows Jenny is mad. She will be confined to a mental hospital and he will discover the cure.

    Next we see Muriel and David in the bedroom with Muriel chained to the bed and David chained to a chair. Stephen drips acid onto Muriel from a contraption and she cries out. David cries out as well, seeing her suffer. Stephen releases him from the chair and he rises, to be pushed onto the bed with her. Still shackled on his feet with wires connected, Stephen turns on a switch which electrocutes them both in bed. They cry out.

    Stephen is seen removing her heart from her corpse, which he places in a water tank along with the heart of David. Next we see her ashes placed in an urn with a strange plant.

    Stephen arrives at the castle with Jenny, who he has just married, having gotten her from the asylum. Solange is annoyed that he married her against their plan. He consoles Solange (who appears years younger) that once Jenny is insane enough to commit that he will be named over her estate and then Solange will get her money. In the meantime, he will see to it that Jenny goes mad.

    He prepares a hallucinogen to be added to Jennys drink which Solange adds. That night Jenny hears two hearts beating and gets up. She opens a door to find wind and a laughing woman's voice. Seeing the plant, which has almost bloomed, she notices drops of blood beside it. She gets back in bed with Stephen, who pretends to be asleep. Later she tells him about her dream and the blood. He tells her it is only a nightmare.

    Jenny and Stephen are seen at a fountain with white doves. Jenny asks questions about Muriel and Stephen fills her in. She apologizes to Stephen for her outburst last night. He tells her if could be nothing other than delirium, which he hopes will not happen again. Solange comes to tell him that the lab is ready. He goes with her, leaving Jenny at the fountain.

    In the lab, he finds that one vial is still present in the cabinet: the vial of hallucinogen that Jenny was supposed to have received last night. Solange apologizes and says it couldn't be. He insists otherwise, but tells her that regardless, Jenny seems to not need the drug to go over the edge. He kisses Solange.

    Jenny finds the sheet music on the piano and asks if Muriel wrote it. She is told that Muriel occasionally did write music. Jenny attempts to play the theme. As the music plays, she seems to become more like Muriel and asks for a drink. The servant brings it, and she remarks that she likes it. Stephen throws down a medical journal that he doesn't care for and complains about the doctor who wrote it. After the music has stopped, he notices that Jenny is gone. He and Solange go to her room, but she is not there. Then a scream is heard. Solange says that it comes from below. They head toward the passage leading down to the crypt. Another scream is heard before they reach it. At the bottom of the stairs, they push open a door to find Jenny white as a ghost, collapsing. Stephen carries her up to her bed. They discuss what happened and she cannot remember parts of it, only that her hands were bloody and she tried to remove the covering to the crypt. He tells her it was all in her imagination. She insists that the door to the crypt was locked, but he says no, it was easily opened when he pushed on it. He tells her that her condition frequently causes things to seem impossible. She begs him not send her back to the asylum and he agrees, but tells her he wants her to get better. Dr. Joyce (Marino Masé) will come and take care of her, since he did for so many years at the hospital.

    When Dr. Joyce arrives, he is greeted by Stephen and Jenny, who tries to sweep him away to the woods. Stephen intervenes, suggesting that the doctor has just arrived. Dr. Joyce says it is all right, but Jenny agrees that her husband is right, leaving and going inside.

    Dr. Joyce talks to Jenny about remembering all that has happened to her. He says Stephen has told him everything that has happened recently. She remembers something about David but gets confused. He asks what happened. She tells him that someone else takes over her mind and that then she gets confused. She remembers the crypt and the greenhouse, so they go there in an effort to remember. She says someone was kissing her, but she cant remember who. Someone else came in and struck him. She tells Dr. Joyce that she lost an earring which should be in the leaves below. When he finds it, she seems to recognize it but then when questioned further becomes confused. He suggests maybe she lost it another time. Then she admits that it is not her earring and she has never seen it before.

    In Dr. Arrowsmiths study, Solange breaks a bottle and he chides her, telling her he was able to restore her youth but not her mind. She reminds him that it is not her mind that he needs. Dr. Joyce comes in to discuss Jennys condition, showing him the earring that she found in the greenhouse. Stephen tells Solange to go find the other earring in Jennys room. Going to a secret location, Solange gets the other earring and goes to Jennys room (which Stephen says has changed per Dr. Joyce). She slips it into the jewel box and tells Jenny the Doctor wants to see it. When Jenny shows her jewelry to Dr. Joyce, she finds the other earring and becomes confused. Stephen brings over the other one, explaining that they are Muriels earrings and that Jenny has never worn them. Confused, she leaves the room.

    At dinner, Dr. Joyce is discussing wizards and witches of Africa who made contact with the dead, when suddenly Jenny rises, announcing she is tired and will turn in. Stephen tells her he will follow immediately. Jenny leaves and the doctors discuss her condition. All at once Solange cries out, having apparently cut herself. Stephen attends to her, telling Dr. Joyce he will have to take her to the lab to prevent a hemorrhage. He explains that she has a rare blood disorder but that it is nothing. As they leave the room, Dr. Joyce notices her place at the table, looking closely at it. The butler comes in and asks if he wants anything, to which he replies no. Announcing that he will go to his room, he leaves. The butler also looks at the place he was looking.

    Upstairs, Dr. Joyce finds his room locked and knocks, asking who is there. Behind him there is a noise and he looks around to find a passageway opening in a panel in the wall. He goes through.

    In the lab, Stephen tells Solange that they will need new blood. He draws some from a container and gives her an injection. He says this worked for now but soon they will need some new solution.

    Jenny awakens to the sound of the hearts beating. She hears Muriels voice telling her that her blood is being used down in the laboratory and to hurry. Jenny gets up and begins to go.

    Dr. Joyce finds himself in the crypt looking at graves. He finds Muriels crypt and the lid slides over, revealing it to be empty.

    Jenny enters the lab and picking up a scalpel, he goes to attack Stephen, who is attending to Solange. Solange cries out as she sees her coming. Striking his face with the scalpel, Jenny renders a cut on Stephen just as Dr. Joyce enters. He takes Jenny back to her room. Solange tells Stephen that it was not the face of Jenny but Muriel.

    In her room, Jenny draws Dr. Joyce to sit in bed with her. He speaks to her and she looks strangely at him, asking who he is. She tells him she is not Jenny, but Muriel and kisses him. Again he calls Jenny and she kisses him again. Suddenly the doors fly open and a breeze blows through. Seeing no one, Dr. Joyce returns to Jenny, who asks if he saw what she saw. He tells her that he will find out what it was. In the greenhouse, Jenny asks the doctor what Muriel wants with her. He tells her that she must leave these surroundings in order to get better.

    Solange tells Stephen that the doctor is now a threat and cannot be allowed to leave the castle. He agrees with her. At that moment Dr. Joyce enters and asks to speak to him. Solange leaves. He tells Stephen that he will take Jenny back to the clinic in the morning so she can get better. Stephen agrees and Dr. Joyce retires to his room, beginning to write. Next he calls the butler to prepare his bath. Meanwhile Stephen drills a hole in the wall in the bathroom and connects wires to electrocute Dr. Joyce when he steps into the tub. Before Joyce can do that, the butler returns with towels and fixes them on a rack by the tub. As he brushes by the tub, he accidently knocks the soap bar into the water. Hearing activity, Stephen prepares to throw the switch and does. When he reaches for the soap he cries out as he is electrocuted. Dr. Joyce removes him and next they are seen discussing his death. Joyce pronounces a heart attack and Stephen tells Solange to take Jenny away.

    Stephen asks Joyce to prepare a death certificate and help move his body back to his room. When that is done, Joyce wants to light a candle for the dead while Stephen leaves. After they both leave the room, the butlers hand falls to the side, revealing a burn on his wrist from the electric shock.

    Solange meets Stephen in the hall, confessing she is frightened and uncertain of what to do now. He reassures her everything will go as planned. He goes to speak to Jenny, telling her she has been through a shock. She says she is anxious to leave in the morning with Dr. Joyce. At this point he turns on her, accusing Dr. Joyce of manipulating her because she is weak, beautiful and rich. She swears he has done nothing wrong and that they have been friends for many years. He tells her he saw them holding hands in the greenhouse and that he doesn't want to lose her. He persuades her to come with him to Spain or Italy and she agrees.

    Next we see Dr. Joyce reluctantly telling Jenny that it will be good for her to go elsewhere. She acts as if he might be talking down to her. He tells her he will be leaving in the morning, but that he is very fond of her and if she ever needs anything for her to call upon him. She cries.

    That night she is dreaming as Muriel again and Dr. Joyce comes in and observes her as she writhes. He asks if it is Muriel and asks where her body is and who killed her. When Stephen comes into the room, he hides behind draperies. Jenny screams when she sees Stephen.

    Solange begs Stephen for the blood of Jenny to replenish her, saying that Muriels blood is heavy within her, like mercury. He promises that Jennys blood will be available soon.

    Next morning Dr. Joyce is saying goodbye when Jenny approaches and asks why he is leaving. She asks him if he likes the Hampton Crest which is at the base of a statue of two lovers. She seems more like Muriel. He bids them goodbye and leaves. Solange seems in pain waiting for the new blood.

    Jenny is seen in her room, packing. Thunder is heard outside. Jenny approaches Stephen and calls him. He comes toward her with a murderous look and slaps her down. Grabbing her, he tells Solange to come to the lab. Meanwhile in the rain we see Dr. Joyce who has returned and enters the castle. Inside, he looks at the Hampton Crest, finally turning it clockwise, which opens a cabinet door. Inside is the container with the two hearts of Muriel and David. He carries it to the desk and removes the dagger. The cries of Muriel and David are heard by Dr. Joyce and seen looking down from a high position.

    In the lab Stephen tells Jenny that her sister is calling her and that we will no longer have to deal with hearing her cries anymore. Solange cries out that she cant stand it. Stephen brings cotton dipped in ether and puts Jenny to sleep. Solange is told to lie on the other berth. After they are connected with tubes, Stephen tells Solange it will take about two hours and for her to remain still while he prepares for the trip the three of them will make.

    Stephen comes out and sees Muriel and David with their wounds, facing Dr. Joyce. Stephen hits Joyce from behind with a candlestick, knocking him out. Muriel takes Stephen aside, telling him she will help him see the ecstasy of pain and death that she has. As he pulls her hair aside, he sees her hideously deformed face. She laughs and secures him in the chair, throwing a candle and setting him on fire. Meanwhile David enters the lab and Solange, seeing him, screams. He cuts the blood line, laughing, and it drips on the floor. Next we see Stephens chair with his body completely burnt up. Muriel stops laughing. Solange is shown back in her old body again as David laughs, destroying the lab equipment. Next we see Solange as only a skeleton.

    Dr. Joyce recovers and stands up. David approaches Jenny on the table and shakes her. She awakens and screams. At this point Dr. Joyce comes in and pulls David away into the lab which is filling with smoke. He picks Jenny up and carries her out. Upstairs they lock the doors to keep David out and turn to run. Jenny is horrified to see Muriel coming toward them. David breaks the doors open and comes in. At this point Dr. Joyce takes the two hearts and throws them into the fire. As they burn, Muriel and David disappear. Dr. Joyce and Jenny run outside into the rain. As they pause and look back, he tells her she is safe now and will have no more problems from Muriel. The two hearts are shown again burning in the fireplace.