The Achtung! Cthulhu 2d20: Gamemaster's Guide is a 200+ page resource for running the "Secret War," a pulp-horror RPG setting blending WWII with Lovecraftian terror. The guide provides extensive lore on factions, including Black Sun and Section M, alongside GM tools for managing "Threat," strange weapons, and bestiary entries. The official digital version is available from Modiphius Entertainment . Achtung! Cthulhu 2d20: Gamemaster's Guide - PDF