Recommended reading: The Ninth Configuration (1966):

The Ninth Configuration

aka Twinkle, Twinkle, "Killer" Kane.

By William Peter Blatty.

Paperback.

Published in 1966.

ISBN-10: 0765337304

ISBN-13: 978-0765337306

Description:

Hidden away in a brooding Gothic manor in the deep woods is Center Eighteen, a secret military "rest camp" currently housing twenty-seven inmates, all officers who have succumbed to a sudden outbreak of mental illness. Have the men truly lost their minds, are they only pretending to be insane to avoid combat, or is some more sinister conspiracy at work?

Desperate for answers, the Pentagon has placed a brilliant Marine psychiatrist in charge of the base and its deranged occupants. A man of deep faith and compassion, Colonel Kane hopes to uncover the root of the men's bizarre obsessions. But as Center Eighteen descends into chaos, Kane finds the greatest challenge may be his own buried demons. . .