Mi-Go... now there's an idea. Another player has already (unknowingly) angered a Shub-Niggurath cult by destroying one of her idols, so perhaps this cult also has contact with the fungi from Pluto. It could be that the Mi-Go periodically visit the temple looking for significant minds to kidnap and stuff into cylinders; the player has a boyfriend who disappeared in the area, he could have been one of the ones taken. The PC could learn that his boyfriend is still alive (in some capacity) from the cult that's going to be hunting the group.
Thanks for the inspiration!