"The Recurring Doom" is a Cthulhu Mythos short story by S. T. Joshi, first published in 1980.
Synopsis[]
Jefferson Coler is a prestigious but controversial British archaeologist with a strong interest in arcane books and ancient languages. In 1940, after returning from an expedition to Arabia, he calls his colleague Collins (the narrator), to show him a strange object he had found while excavating the ruins of what might have been legendary Irem, the City of Pillars. The object is a green rectangular crystal, similar to a box, but with no openings, and made of an unknown material that laboratorial analysis failed to identify. On the next week, Coler contacts Collins again to show him that the interior of the crystal is now glowing, as if a small luminous object had formed inside it.
Faced with this inexplicable phenomenon, Coler and Collins search in several occult books for an explanation, but are unable to find anything about it in De Vermis Mysteriis, the Unaussprechlichen Kulten, the Civitates Antiquae Fantasticae, or the Necronomicon. However, Collins' attention is drawn by a newspaper article about a congregation of cultists performing some sort of ritual in the druidic megaliths of Sentinel Hill, Brichester.
At this point, their research is interrupted by the arrival of Joseph Meredith, head of the Archaeology Department at Miskatonic University, who traveled to Britain to ask for Coler's help in deciphering the language of a parchment found recently in Egypt. While Coler studies this new text and Meredith rests from the long trip, Collins returns to his studies. With Coler and Collins focused on their tasks, the house is invaded by a cultist bent on stealing the crystal. Collins attacks the intruder and prevents the theft, then follows the man all the way to Sentinel Hill, where he sees that the cultists are gathered again, and witnesses the would-be thief being severely beaten by the cult leader for his failure.
On the next day, Collins finds that Coler's house has been broken into again, the crystal has been stolen, and Coler is unconscious, a wound on his head showing that he's been knocked out. Collins revives him and tends to his wound. As soon as he recovers, Coler grabs a rifle and tells Collins that the cultists must be stopped at any cost. Collins asks about Meredith, and is told that he has gone back to Arkham after finding out that a number of young people, including Miskatonic students, have been found dead in the sea off the coast of Innsmouth, their bodies torn apart viciously as if by some clawed animal, and covered in foetid slime. A similar incident has also happened in Tahiti.
Armed with Coler's rifle, Coler and Collins rush to Sentinel Hill, where the cult leader is presiding the ceremony and the crystal is already in place, the glowing sphere in its interior having increased in size visibly. Coler shoots the cult leader, fights the cultists alongside Collins, and retrieves the crystal. After that, the two take Coler's car and drive to an abandoned mine shaft, where Coler throws the crystal into a deep pit.
On the following day, Coler explains to Collins that his translation of the Egyptian parchment had revealed the answer to the enigma. All over the world, there have been reports about the rise of mysterious cults, culminating in a series of assassinations, disappearances and less explicable occurrences, from dolphin uprisings in California to the sighting of strange objects in the Pacific. According to Meredith's parchment, the Earth was once inhabited by the servitors of Azathoth, but was taken from them by Cthulhu and his Deep Ones, so the forces of Azathoth retaliated by imprisoning Cthulhu under the sea. The pre-human worshipers of Cthulhu used elements from Yuggoth to forge the Crystal of Zamalashtra, and preserved the knowledge that when the stars were right, the interior light would glow, and the crystal could then be used to release Cthulhu.
Coler assumes that "when the stars are right" refers to the alignment of Yuggoth, which he claims to be the planet Pluto, the orbital period of which is 248 years. Therefore, he reasons that the stars are "right" every 248 years, and that the last time it happened was in 1692, the year the Salem witch trials took place, presumably in response to the increased activity of sorcerers. Coler and Collins are relieved to know that it won't happen again in their lifetimes, but are also aware that at some point, the crystal will be found again, and if it ever falls into the wrong hands at the wrong time, the consequences will be devastating.