Antagonist
Character Role Analysis
None
There's really no villain or antagonist here, folks. Dr. Crane probably comes closest, but he's only in a small fraction of the book, and Louis is a huge fan, so that seems unfair to the good Doctor. The book's primary tensions seem to exist among the protagonists, but none of them occupies a clear villain role.
You could make an argument for death being the real antagonist, we're going to play by the rules and say that, because death isn't an actual human, it can't be an antagonist. Sorry, death, you lose again.