Mrs. Which confirms that Meg and Charles’s father is indeed fighting the Dark Thing. He is presently behind the Dark Thing, Mrs. Which adds. When Meg begins to cry at this news, Mrs. Which tells her not to despair. There is always hope; this is why they are here.

Then Mrs. Which tells them it is time to travel on. Before they go, she attempts to explain how they tesser. Mrs. Which uses the example of a small insect trying to travel the length of a long piece of material. If the insect continued in a straight line, it would eventually get to the other side but doing so would take a lot of time. Then she says if the material were folded so that the far end was brought to the point where the insect was sitting, the journey would take only a second or two. That is what happens when they tesser: time and space are folded. This is done in the fifth dimension.

Charles Wallace tries to explain to Meg what the fifth dimension is. Meg says she knows the third dimension is the square of the second, and the fourth dimension, which has something to do with Einstein and time, is the square of the third. Charles fills in the rest of the information by stating that the fifth dimension is the square of the fourth, and it is called a tesseract. That is what their mother and father had been investigating.

Although this information is not entirely clear in Meg’s or Calvin’s minds, the children prepare for another journey. This time Meg is not as frightened. She is able to relax until she is about to rematerialize and finds that there is too much pressure being applied on her chest, and she can barely breathe. Then she hears someone say there has been a mistake. Mrs. Which has attempted to land on a two-dimensional planet. She had forgotten the children were three-dimensional beings and could not exist in a two-dimensional environment. Mrs. Which quickly changes their direction. When they fully rematerialize a few seconds later, they discover that they are somewhere in Orion’s belt. There is a friend of Mrs. Which’s who lives there, and Mrs. Which wants the children to meet her. Her friend’s name is Happy Medium.

Happy Medium lives in a dark, cold cave. As the children come upon her, she is standing in front of a large bonfire she has set to keep the children warm. She is also staring into a huge crystal ball. When Mrs. Which asks Happy Medium to show Meg, Charles Wallace, and Calvin what Earth looks like through the crystal ball, Happy Medium is reluctant. She says she does not like to look at sad things.

The children move closer to the crystal ball and peer in. When they locate the Earth, they ask why it looks so dark. They are told that the Dark Thing has been moving in on their home planet. This fact has been known for a long time, and there have been many holy people and artists who have been fighting the Dark Think over the centuries—people such as Jesus and the Buddha as well as Bach and Rembrandt.

Meg then asks again where her father is. Mrs. Which says her father is on a planet that has given in to the Dark Thing. Then Happy Medium begins to cry as she prepares to show Meg, Charles Wallace, and Calvin the planet where Meg and Charles Wallace’s father is.