In The Crucible, what does Mary Warren tell Danforth? Why is she in court? Why is Danforth suspicious of her and of Proctor?

Mary Warren is in court because John Proctor has brought
her there to submit her deposition and testify that "She never saw no spirits [...]"
(Act 3).  He is attempting to save his own wife, as well as the wives of Giles Corey and
Francis Nurse, all of whom have been accused of witchcraft by Abigail Williams.  He also
wants the court to understand that Abigail has ulterior motives in her accusations.
 Danforth is immediately suspicious that Proctor's assertion that he only wants to save
his wife is untrue, and so he tells Proctor that Elizabeth is pregnant, and thus will be
saved for at least eight more months.  When Proctor says that he also wants to free his
friends' wives, Danforth with "an almost imperceptible hardness in his
voice" says, "Then your purpose is somewhat larger."  Since he and Parris
believe that innocent people are happy for the courts in Salem, Proctor's
dissatisfaction with court automatically singles him out as a potential problem.
 

Concerning Mary Warren's former statements that people
sent their spirits out on her, she now says, "It were pretense, sir."  She admits that
she lied before, when she accused them, even though she "knew that people would hang by
[her] evidence," according to Danforth.  

Judge Hathorne
instructs her to pretend to faint, as she did before, but she cannot: "I -- have no
sense of it now, I --," she cries.  Finally, when the girls begin to insist that Mary is
sending her familiar spirit to attack them, she calls Proctor "the Devil's man" and
returns to Abby's fold.  

To Proctor, then, Danforth says,
"What are you?  You are combined with anti-Christ, are you not?  I have seen your power;
you will not deny it!" By the end of the act, Danforth is sure that Proctor is in league
with the devil to tear down the courts in Salem.