Mrs. Whatsit, Mrs. Who, and Mrs. Which materialize on Ixchel in response to Meg's summons. However, they insist that they can do nothing to help save Charles Wallace. Mr. Murry requests that they help him with his tessering so he can try to retrieve Charles from Camazotz, but Mrs. Which tells him he will not be successful. Next, Calvin asks to be sent after Charles, but he, too, is refused. After a long silence, Meg realizes that everyone expects her to go back to Camazotz and rescue her brother. Terrified and overwhelmed by the weight of this responsibility, Meg yells that she cannot go back. She gradually realizes, however, that she is the one who is closest with Charles and the one who is therefore most likely to get through to him, to bring him back successfully. Although her father and Calvin do not want to let her go, the Mrs. W's ultimately convince them that it is for the best.
Meg says goodbye to her father, Calvin, and Aunt Beast, and also apologizes to her father for her accusatory outbursts. Mrs. Which tells Meg that she will tesser with her through the Black Thing so that Meg will arrive at Camazotz safely. Once again each of the Mrs. W's presents Meg with a gift: Mrs. Whatsit enhances the force of her innate love; Mrs. Who gives her a blessing from the New Testament; and Mrs. Which strengthens in her the one thing that she has that IT has not. However, Meg must discover this thing for herself.
After tessering with Mrs. Which, Meg arrives safely on Camazotz and heads directly to the domelike building where IT lies waiting. Inside, Charles Wallace crouches behind the dais containing the disembodied brain; his eyes roll and a tic in his forehead pulses to IT's revolting rhythm. Meg tries to identify Mrs. Which's gift, while Charles insists that she has nothing that IT does not also have; her weapon cannot be her ability to resist, her anger, or her hatred, for IT has all of these things.
Charles tells Meg that Mrs. Whatsit hates her, and at that moment, Meg realizes the one thing that she has that IT does not have: love. Though she cannot possibly love IT, she can love Charles Wallace, and she calls out to him with the force of her love. Suddenly, he runs into her arms and the children tesser together through the darkness. When they emerge from the darkness, they find they have rejoined Calvin and Mr. Murry in the twins' vegetable garden back on Earth!
After a joyous family reunion, the three Mrs. W's appear. Mrs. Whatsit apologizes for not saying goodbye; the Mrs. W's are busy with a new mission. She starts to describe the mission, but at that moment there is a gust of wind and before Mrs. Whatsit can complete her sentence, the three extraordinary ladies are gone.
All of the gifts that Meg receives in this chapter allude to Christian theology. Mrs. Whatsit and Mrs. Which strengthen Meg with both their love and her own love, and Mrs. Which gives her an excerpt from St. Paul's Epistle to the Corinthians. This Biblical passage offers empowerment to the foolish and the weak and charges human beings to fulfill their calling despite their sense of inadequacy.
Left to discover Mrs. Which's gift for herself, Meg gains the power of free choice. Throughout her novel, characters make small but important decisions that affect the entire universe: these include Charles Wallace's decision to visit Mrs. Whatsit, the children's decision to make the journey, and Meg's return trip to Camazotz. In empowering her characters with freedom of choice, L'Engle rejects notions of determinism. She believes that life is like a sonnet--organized and structured, but not pre-determined. As Mrs. Whatsit tells Calvin, "You're given the form, but you have to write the sonnet yourself. What you say is completely up to you." When Meg decides to return to Camazotz, she writes another line in the sonnet of her life.
Meg returns to Earth a changed person, even though no chronological time has elapsed. Finally confident in who she is, she understands that she does not need to conform in order to make positive contributions to the world. Meg discovers that the power of selfless love can set her free just as it released Charles Wallace from the clutches of IT. Thus, her cosmic quest to prevent the Dark Thing's conquest of the universe is also a deeply personal quest: having successfully completed it, Meg is able to accept herself and her own abilities; she is ready to make her own contribution to the world.