Gurps Cabal by Kenneth Hite

A role-playing sourcebook that lays out a modern occult-conspiracy campaign setting centered on an international secret society locked in a millennia-old struggle with rival cabals, supernatural powers, and cosmic horrors; it supplies extensive background on hidden histories and secret groups, ready-made NPCs and organizations, rules and examples for rituals, sigils, artifacts and monsters, scenario seeds and maps, and guidance for running paranoid, occult-horror games that mix real-world conspiracy theories, mythic lore, and Lovecraftian-style threats.