This massive, full-color volume is filled with deep resources just for the Delta Green game master. THE PAST: details on the world and history of Delta Green. THE UNNATURAL: details on the Cthulhu Mythos, from monsters to hypergeometry to the Great Old Ones, including rules for creating new threats. THE SCHISM: deep details on the Delta Green organization itself—or rather, two different Delta Green groups, not always working to the same ends. THE OPERA: guidelines for creating scenarios, running campaigns, and customizing the setting. APPENDICES: a ready-to-play scenario, “The Sentinels of Twilight,” a Handler-facing glossary, index, recommended media, sample NPCs to use in any game, rules variants, and more.