What is the fine-grained topic of the following text: A world being taken over by a plague, a deadly infection, and your choice is either to become a Weeper (a zombie-like existence), to die, or to give yourself in servitude to the Silver (a vampire-like race), who are the only thing standing between some sort of life and certain death. Only return the topic.
Post-apocalyptic world with plague, zombies, and vampires