Xenocide by Orson Scott Card
Xenocide is the third of the Ender books. (Here’s my review of the second, Speaker for the Dead.) The title literally means killing a stranger, but in the series means the equivalent of genocide, except killing an entire alien species instead of a race of humans. It picks up a lot of loose threads from Speaker for the Dead, and a reader who hasn’t read that volume might be lost.
There are a lot of philosophical and metaphysical discussions in the novel as characters work together to solve scientific problems and ethical dilemnas. Among the themes and issues debated are sacrifice, slavery, biological determinism, and the nature of God. They solve their problems by figuring out a way to escape natural law and travel faster than light, and in so doing, get a couple surprises. It’s really the kind of book that can make you think abstractly in a challenging way, but if abstract concepts bore or confuse you then this is not the book for you. In addition to characters from the other Ender books, this novel introduces the world of Path, where people follow a fundamentalist religion, led by people with OCD who they call “godspoken” because they believe that the gods speak to them through their disorder. I enjoyed it and the next book, Children of the Mind, is on the list!