A device that lets people communicate across alternate timelines causes people to consider the nature of free will and the relationship between one’s actions and one’s character.
Chiang takes a relatively abstract concept and pins it down to several very specific and complicated characters who are navigating thorny concepts of morality and ethics, with a nice little tale of betrayal and subterfuge tying them all together. It’s his ability to populate heady, high-concept stories with distinctive and realistic characters that make’s Chiang’s stories especially effective.