The sentence in this excerpt that shows a simile is:
"He kept his eyes fixed on her, marveling at the way her face changed with each turn of their talk, like a wheat-field under a summer breeze."
In this part of the sentence, the author is comparing the face with a wheat-field.
A simile is a figure of speech that compares two different things using the words "like" or "as" to reflect the comparison. A simile is different from a metaphor since the simile uses "like" or "as" whereas a metaphor just states the comparison.