In Act 3, Scene 2 of "The Crucible," Mary Warren tells Danforth that she and her friends did not really see spirits and that they were lying when they said they did. She tells him this in person after he rejects her signed deposition stating the same.
Mary's confession threatens to undermine the entire witch-hunt, in which Danforth, as judge, has played a key role.
He suspects that John Proctor is attempting to interfere with court proceedings by telling Mary to recant her earlier testimony. As such, Danforth cautions the girl that she will be imprisoned for doing so, regardless of whether she is now telling the truth, since contradictory testimonials indicate perjury.