This is a sourcebook for Call of Cthulhu to be used in a modern day setting. It reimagines the Mythos for a world of conspiracy theory and political intrigue. Specifically, investigators are affiliated with a conspiratorial group, Delta Green, that is linked to intelligence, law enforcement and military organizations of the United States. The mythos of UFO's and modern conspiracy theory is merged with the Lovecraft Mythos.

This is an alternate setting for CoC licensed through Chaosium and so uses the BRP game mechanics. There are notes on how the Mythos plays differently in the DG setting than in standard CoC games, new skills related to black ops and espionage, backgrounds on Delta Green, Majestic-12 and other conspiratorial organizations and their chief NPC's, an appendix on security classifications, expanded firearms lists and rules, two adventures and an outline for a campaign.