The Crucible takes place in Salem, Massachusetts in 1692. The action begins in the home of Reverend Parris, whose daughter Betty lies unconscious and appears very ill. Around midnight the night before, Parris had discovered Betty, his niece Abigail, and Tituba, his black slave, dancing in the woods, causing Betty to swoon. The local physician is unable to determine the cause of Betty's illness. Mr. and Mrs. Putnam arrive and reveal that their daughter Ruth is also ill. There is talk in the village of an unnatural cause.
Abigail warns her friend Mercy Lewis and the Proctors' servant Mary Warren, not to reveal that they were all casting spells in the woods. Betty wakes, and Abigail threatens the other girls with violence if they tell anyone that she drank blood and cast a spell in order to kill Goody Proctor. Betty loses consciousness again.
John Proctor and Abigail talk privately about their former relationship. Prior to the opening of the play, Abigail worked as a servant in the Proctor home. Elizabeth Proctor was ill at the time and Abigail took on more responsibility within the Proctor household. When Elizabeth discovered the affair, she dismissed Abigail. During their discussion, Abigail becomes angry with Proctor because he refuses to acknowledge any feelings for her.
Betty wakes again and is hysterical. The well-respected Rebecca Nurse is visiting the Parris household and calms her. Prophetically, Rebecca warns Parris that identifying witchcraft as the cause of Betty's illness will set a dangerous precedent and lead to further problems in Salem. Mr. Putnam asks Rebecca to visit Ruth and attempt to wake her. Ruth is the only Putnam child to survive infancy, and Mrs. Putnam is jealous of Rebecca because all of Rebecca's children are healthy, whereas Mrs. Putnam had lost seven infant children.
Putnam, Proctor, and Giles Corey argue with Parris about his salary and other expectations. Parris claims that a faction is working to drive him out of town, and he disputes their salary figures. Putnam, Proctor, and Corey then begin arguing over property lines and ownership. Putnam accuses Proctor of stealing wood from land that he does not own, but Proctor defends himself, stating that he purchased the land from Francis Nurse five months ago. Putnam claims Francis had no right to the land and, therefore, could not sell it.
Reverend Hale arrives from another town to investigate the strange events in Salem. The people of Salem have summoned him as an expert in witchcraft to determine if witchcraft is behind the children's illnesses. Hale learns that the girls were dancing in the woods with Tituba, and that Tituba can conjure spirits. Abigail blames Tituba for enticing her to sin. Hale then questions Tituba, and she admits that she has seen the Devil, as has Goody Good and Goody Osburn. Abigail also confesses to witchcraft, stating that she had given herself to the Devil, but that she now repents. Betty wakes up, and she and Abigail name individuals that they say they have seen with the Devil.
Eight days later, Elizabeth discovers that Proctor spoke to Abigail privately while in Salem. Elizabeth and Proctor argue over this. Mary Warren comes home from Salem where she is serving as an official of the court, and gives Elizabeth a poppet (doll) that she made for her while sitting in the courtroom. Mary Warren tells Proctor that some of the girls accused Elizabeth of witchcraft, but the court dismissed the charge because Mary Warren defended her.
Hale arrives at the Proctor house and questions Proctor about his poor church attendance. He asks Proctor to name the Ten Commandments. Proctor names nine successfully, but he forgets the commandment forbidding adultery. Hale questions Elizabeth as well. Proctor reveals that Abigail admitted to him that the witchcraft charges were false.
Marshal Herrick then arrives and arrests Elizabeth. Earlier that evening, Abigail feels a needle-stab while eating dinner, and she accuses Elizabeth of attempted murder. The authorities of Salem search the Proctor house and discover the poppet, along with a needle. Hale questions Mary Warren and learns that she sewed the poppet and stored the needle inside. Mary Warren also tells him that Abigail saw her sew the poppet and store the needle. Nevertheless, Elizabeth is arrested.
The court convicts Martha Corey and Rebecca Nurse of witchcraft. Giles Corey tells the court he has proof that Putnam is accusing his neighbors of witchcraft in order to gain their land. Judge Danforth asks the name of the witness who gave Corey the information, but Corey refuses to cooperate. The court arrests him. Judge Danforth informs Proctor that Elizabeth is pregnant.
Mary Warren tells the court that she pretended to see spirits and falsely accused others of witchcraft. She reveals that Abigail and the other girls are also lying. Abigail denies Mary Warren's charge, however, and she and the others claim that Mary Warren is sending out her spirit against them in the court.
Proctor denounces Abigail's charge against Mary Warren, stating that Abigail is a lying whore. Proctor informs the court of his affair with Abigail and states that she is lying in order to have Elizabeth executed, thereby providing herself with the opportunity to become his wife. After Proctor agrees that Elizabeth would never lie, the court summons Elizabeth and questions her about the affair. Not knowing that her husband has confessed it, Elizabeth lies about the affair and is returned to jail. Abigail resumes her claim that Mary Warren is attacking her until Mary Warren recants her confession that she lied about the witchcraft and charges John Proctor as the Devil's man.
Several months pass. Proctor is in prison, scheduled to hang, along with Rebecca Nurse. Elizabeth is also in prison, although the court has delayed her execution until after she gives birth. Hale attempts to convince the prisoners to confess rather than hang, but all refuse. Proctor confesses and signs a written affidavit, but he destroys the document rather than have it posted on the church door. Proctor is taken to the gallows.