Mrs. Which replies that Meg is correct. Her father is behind the darkness so they cannot see him. Mrs. Whatsit tells Meg not to despair. There is hope, even though the task is difficult. They must go behind the shadow, and to do that they must tesser again. She explains what tessering is. It is like taking a short cut between two points. Mrs. Who demonstrates by taking hold of a part of her skirt in her left hand and another part in her right hand, and then bringing her hands together. Meg doesn't understand, but Mrs. Whatsit explains that they travel in the fifth dimension of space. She tries to explain to Meg the concepts of one-dimensional, two-dimensional and three-dimensional. The fourth dimension is time. The fifth dimension is a tesseract. Add that to the four dimensions and travel through space is possible without having to go the long way round.
One by one, Mrs. Whatsit, Mrs. Who and Mrs. Which disappear as they tesser. Then there is darkness and utter silence. Meg's body seems to dissolve. She feels great pressure and her lungs are squeezed together. Her mind is flattened out and she cannot think. Then she hears a voice saying they have stopped by mistake at a two-dimensional planet and must move on. Then the nothingness returns, after which she is pushed out of the fifth dimension with a jerk, and she sees Calvin and Charles Wallace again. Mrs. Which apologizes for her mistake, and Mrs. Whatsit tells them they are now in Orion's belt. When Meg worries that their mother must be frantic over their absence, Mrs. Whatsit reassures her: they did a time wrinkle as well as a space wrinkle, so when Meg returns, it will be about five minutes before she left.
They all take a walk. The planet they are on is very flat, with no vegetation. They go into a cavern and meet a woman called the Happy Medium, who is gazing into a crystal ball. Mrs. Whatsit asks her to show the children their own planet. Meg looks into the crystal ball, sees the Milky Way, then Mars, then the Earth, but Earth is covered by a smoky haze. The shadow that darkens the earth is the same Dark Thing they perceived on Uriel. Mrs. Whatsit says it has been there a long time, and that is why the earth is so troubled. Mrs. Which says the Dark Thing is Evil, the Powers of Darkness. She says they will continue to fight it. The battle is being fought all over the universe. Coaxed by Mrs. Whatsit, the children realize that on earth it has been fought by people such as Jesus, Shakespeare, Einstein, Buddha, St. Francis, and many others. Mrs. Whatsit then says that their father is on a planet which has given in to the Dark Thing.
In this chapter, L'Engle makes imaginative use of the theories of physicist Albert Einstein. Einstein's special theory of relativity (1905) and general theory of relativity (1915) revolutionized the way scientists understood the physical universe. According to Einstein's theories, space is not three-dimensional and time is not a separate entity. Together they form a four-dimensional continuum called "space-time." Some people believe that Einstein's theories demonstrated that time travel, at least in theory, was possible. L'Engle insisted that the scientific concepts in her book were accurate, although the reader does not need to understand these concepts in order to enjoy the book. Science fiction writers have long envisioned humans traveling through time and space into distant corners of the universe, and scientific theories pale before the vistas that can open up to anyone with a fertile imagination.
The battle in the universe between good and evil is made explicit in this chapter, and shown to be the cause of strife on earth. It is easy to see why the children name such historical figures as Jesus, the Buddha, and St. Francis as being fighters against evil, but why are artists, writers and musicians included as well? The names Leonardo da Vinci, Shakespeare, Beethoven and Rembrandt are mentioned. This is because these men expressed their individual creativity. They expressed themselves in their work. The significance of this will become apparent when in the next chapter the children arrive on Camazotz, and discover what happens when individuality and creative expression are suppressed.