In Ch. 5-8, what has happened to Meg's father in A Wrinkle in Time?

Megs father was captured by It
on the planet Camazotz.

Megs
father has disappeared and no one knows where he is.  Megs 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 Megs 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 Megs
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 Shakespeares
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 Megs 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 fatherand
her brother.