As World War II rages, the SS Karotechia, is calling upon the obscene powers of the Cthulhu Mythos to ensure a Nazi victory, meddling in powers they do not understand and cannot hope to control. Now a Karotechia defector brings news of Thule, the Nazi Atlantis, legendary home of Aryan super-beings who ruled pre-history. Thule was supposed to be a Nazi myth, but the defector brings proof of Thule’s reality. Delta Green’s course is clear: the alien city and its technological and occult secrets must be denied to the enemy. But the true masters of Thule are fighting their own war. A traitor from the past endangers their eons-old plan to shape the future. The survival of mankind depends of the fate of Thule; but to destroy Thule or save it? Which choice will save mankind? The men and women of Delta Green will be tested to their limits to hold the apocalypse at bay. These are the glory days of Delta Green. They are also humanity’s darkest hour.