This book tried to do a lot, and achieved a good chunk of that. It’s about a generation ship that is so old no one remembers how it got started. It tootles along through the galaxy with a strictly delineated upper class and lower class. There is a failed mutiny. They explore a spooky abandoned planet on which something awful happened. An alien ship appears that foils all of their attempts at understanding. It’s so alien they are really not sure if it even knows that they are there. Religious people Have Opinions about all of this and are an entrenched power structure on the ship. The ending is vague which I sort of liked but also after all the build up sort of didn’t.