What is the theme in That Hideous Strength by C. S. Lewis?

The theme of good versus evil is evident thought the entire novel. Near the beginning, the reader gets a sense that the people within the N.I.C.E. do not have aims that are good. Their descriptions of the future they hope to achieve offend the conscience upon reading them. It takes a little while longer for the "good" characters to fully define themselves to the reader, but when Jane goes to St. Anne's with the news of a disturbing dream she has had, the reader guesses that this group is good. Upon meeting with Dr. Ransom Jane undergoes some transformations within herself that show she has grown as a person because of this interaction. The two sides could not be more different from one another. The N.I.C.E. is a hierarchal institute, while St. Anne's is based on egalitarian principles.