Discover a world where war is a geological era. Explore the Grey Zone, survive the Rain of Teeth, and uncover the truth of the Iron Harvest in this dark industrial sci-fi mystery. Industrial sci-fi series, dark military science fiction, post-apocalyptic mystery books, Eternal War Chronicles. Grimdark world-building, stories about sentient machines, books like Warhammer 40k and Dune, subterranean sci-fi novels.