In Arthur Miller's The Crucible, Mary Warren is caught up in the witchcraft hysteria of Salem, Massachusetts. She becomes part of a group of girls led by Abigail Williams who behave oddly and claim to be tormented by witches. They also directly accuse various people in their community of being witches and torturing them.
At first, when Betty Parris begins acting strangely, Mary is terrified and wants to admit the silly things she and the other girls have been doing. She thinks they will be accused of witchcraft themselves. Abigail tells her to be quiet, but Mary's words may have planted an idea in Abigail's mind right about here. To avoid the charge of witchcraft, they can accuse others, and Abigail has an extra motive that might work out well in the process. Mary just may have unwittingly inspired a plan.
Mary Warren is, for the most part, a rather cowardly girl. She is the servant of John and Elizabeth Proctor, and she seems to be quite scared of them. But as she becomes more and more involved with Abigail and her group, Mary begins to defy the Proctors. She goes to court when she is told to remain at home. She disobeys other orders as well.
Yet Mary is not completely comfortable with what is happening. She still has a conscience, and it is bothering her badly. Although she claims to be affected by the witches along with the other girls, deep down, she knows it is not true. She knows that they are acting, even though their acts are beginning to feel more and more real. Eventually, after Elizabeth is accused, Mary agrees to go with John Proctor to see the judge and tell him what is really going on, even though she is terrified that the other girls will turn on her.
Mary makes a good start. She tells the judge that she and the other girls have all been pretending and lying. She doesn't want to lie any more. But when Abigail enters the court and begins denying her, Mary's courage fails her. She is cowardly once more, and she rejoins the other girls in their playacting, unable to continue to resist Abigail out of fear.
Mary Warren, then, is changeable on the surface as she is led along by events and struggles with her own conscience, but deep down, she does not change, for she is driven by fear and cowardice. She gives into that fear again and again, and her unchanging inability to do what is right shows how much effect fear can have on people who are not strong enough to fight and defeat it. They end up doing things they know are wrong and repulsive.