In a Wrinkle in Time, Why does no one know where Mr. Murry is?

Meg's father is a physicist and worked for the government at a nearby university on several top secret projects. Meg tells him that he had worked in several locations - New Mexico and Cape Canaveral before the family moved here. Soon her father left for business once more. Though his letters had stopped coming a year ago, Meg believes that her mother still writes her father everyday, an expression of “plain, ordinary love” that the other townspeople just can’t understand. Meg tells him of how her mother has pleaded with people in Washington but that all they’ll tell her is that he is on a “secret and dangerous mission” and can’t communicate for a while.