At the end of act 2, when John Proctor's wife, Elizabeth, has been arrested for witchcraft because of the lies Abigail Williams has told, John tells Mary Warren "You are coming to the court with me, Mary. You will tell it in court." Mary is terribly frightened by the prospect...
At the end of act 2, when John Proctor's wife, Elizabeth, has been arrested for witchcraft because of the lies Abigail Williams has told, John tells Mary Warren "You are coming to the court with me, Mary. You will tell it in court." Mary is terribly frightened by the prospect of having to confront the treacherous Abigail, and she says that she "cannot charge murder on Abigail." Proctor, however, is going to force her to tell the court the truth about the poppet found in Elizabeth's possession and the needle Mary stuck into the poppet for safekeeping (the knowledge of which Abigail exploited in order to build a case against Elizabeth).
In act 3, in the court, Proctor tells Danforth that Mary has come to finally tell the truth. She confirms this meekly, saying, "I cannot lie no more. I am with God, I am with God." In order to confirm that Mary is telling the truth now, the magistrates ask her to faint as she fainted before when she says that she was lying. However, she is unable to do it. Abigail and the other girls begin to give the kind of spectral evidence against Mary that they gave against others who have been convicted: suggesting that she's sending her spirit out to harm them. John confesses to his sexual relationship with Abigail in order to prove how devious and deceptive Abigail is. After this, again, Abigail accuses Mary of sending her spirit to "tear [Abigail's] face" as a yellow bird. Mary becomes more and more fearful, understanding to what end Abigail's accusations will lead. John tries to inspire Mary to stick to the truth, no matter how difficult it is, and Mary turns on him to save herself, saying, "Don't touch me—don't touch me! [...] You're the Devil's man!" She now claims that John comes to her at night and tries to force her to sign the Devil's book, that he told her he would murder her if his wife hangs. She says that he forced her to come, saying, "We must go and overthrow the court."
In short, John wants Mary to tell the truth and save his wife, but Mary is more interested in saving herself than telling the truth. She fears Abigail's wrath, and she knows what Abigail is capable of. So she turns on John, accusing him of being in league with the Devil and trying to tempt her to it as well.