If "crisis" in a literary work is "a point of great tension in a narrative that determines how the action will come out," what is the crisis in The Scarlet Letter?
While there can be different interpretations of the "crisis" in The Scarlet Letter, if one considers Arthur Dimmesdale as the character who is pivotal to the theme of Hawthorne that is stated in the concluding chapter,
Be true! Be true!" Show freely to the world, if not your worst, yet some trait whereby the worst may be inferred!
then, certainly, a moment of crisis occurs at the end of Chapter X. For, the devious Roger Chillingworth, who has told Hester in Chapter IV that it is not her soul that he seeks--"Not thy soul...No, not thine!"-- clearly implies that it is her lover's soul that he desires. And, then, in Chapter X as this same Chillingworth insidiously tries to steal within the depths of the minister's heart with his probing questions, such as his asking why the guilty do not avail themselves of the solace of confession, and how a false display of faith can be better than "God's own truth," the unnerved Dimmesdale rushes from the room after exclaiming,
"But who art thou, that meddlest in this matter?--that dare thrust himself between the sufferer and his God?"
After this show of passion, Chillingworth is even more convinced that there is something which Dimmesdale hides: "As with one passion so with another," he says to himself. The physician feels strongly now that there is a "strange sympathy" between soul and body with the minister. So, when the Reverend Dimmesdale falls asleep, Chillingworth stands before him, moves aside the clothing on his chest and views a marvelous sight:
Had a man seen old Roger Chillingworth, at that moment of his ecstasy, he would have had no need to ask how Satan comports himself when a precious human soul is lost to heaven, and won into his kingdom.
But what distinguished the physician's ecstasy from Satan's was the trait of wonder in it!
Now, the reader wonders, indeed, how the plot will develop after this discovery of Chillingworth's. Here the mysterious reference to something on Dimmesdale's chest is a "plant" that will be brought to fruition in Chapter XXIII.