The horrors of the Cthulhu Mythos meet the terrors and intrgues of World War II. The Nazi occultists of the Karotechia think they have unlocked the secrets of legendary Thule, the legendary home of the superbeings that rules prehistory. When a defector brings proof of it to the Allies, Delta Green's course is clear: The alien city and its secrets must be denied to the enemy at all costs.