Meg’s father was captured by It on the planet Camazotz.

Meg’s father has disappeared and no one knows where he is.  Meg’s father is a famous scientist who worked for the government, but he inexplicably disappeared.  No one will tell Meg where her father is, and there are rumors that he simply ran off with another woman.  Meg and her mother know better.  They know his work as a scientist got him into trouble.

It is not until Meg meets Mrs. Who, Mrs. Whatsit, and Mrs. Which that she understands what is going on.  They talk to her about the Black Thing, the evil that threatens Earth and other planets in the system.  She asks Mrs. Which if this is what her father has been fighting when the Tesser, or travel through space and time, on different planets.

"Hhee iss beehindd thee ddarrkness, sso thatt eevenn wee cannott seee hhimm." (Ch. 5)

Meg and the committee of Charles Wallace, Calvin, and the three women/witches/aliens go on a mission to rescue Meg’s father and save the universe.  When Meg asks where her father is, Mrs. Whatsit replies like this.

"On a planet that has given in. So you must prepare to be very strong." (Ch. 5)

Camazotz has a militarized sameness.  Everyone is afraid of not fitting in.  They have to bounce balls in exactly the same way, and do exactly what they are supposed to, or they will risk re-education.  It is on this planet that Meg’s father has been trapped.  The children are forced to go to the planet alone, because the women cannot go there.  They enter the CENTRAL Central Intelligence and see a man with glowing red eyes who can read their minds and talk to them without speaking.  He seems to speak to Charles Wallace, putting a spell on him.  Calvin and Meg escape through willpower and intelligence, but barely.

Meg finds her father and uses her knowledge of Shakespeare’s The Tempest and special glasses given to her by Mrs. Who to get him out of an unusual glass prison. 

In this section, we see how Meg’s faith in her father and her strength helps her get out of sticky situations.  Yet she has always lacked confidence.  She wants to find her father, because he has always been the one person who understood her.  She loves her brother, but he is a complete mystery to her and completely out of her league.  Yet what makes Charles special, also makes him vulnerable to It's manipulation, just as what makes Meg special makes her strong.  She is the only one who can save her father—and her brother.