"The Fire Vampires" is a short story by Donald Wandrei. Written in 1933 alongside "The Tree-Men of M'Bwa", as an addition to the Cthulhu Mythos.
Synopsis
In the distant future, United Federation of Nations historian named Alan Marsdale reminisces of an apocalyptic event involving a comet. A man named Gustav Norby who is on the authority of cosmic lifeforms sees a comet coming on July 7th, 2321, but people laughed him off for these claims as he was trying to warn of impending danger and speculating it's travel. Dubbed 'Norby's Comet', it was speculated to come in 18 years, noted for it's reddish-blue coloration. But in August 10th, on it's arrival to Alpha Centauri, it mysteriously vanished, then appeared 4 days later a billion miles beyond Pluto, perplexing the astronomers and the public and making them theorize it's probably controlled by other lifeforms. With the revelation that it would appear near Earth in 16 hours, it's approach visible from the sky, everyone had mixed reactions from panic to wonderment. People went out to watch it's approach in awe at the dawn of twilight.
Later the comet mysteriously changed it's course and moved at right angles, moving in the opposite direction of Earth's rotation. The comet orbited and illuminated the world, and then it exited orbit towards the direction of Antares after a complete orbit. On August 16th, Norby and his assistant Hue argued about if the comet could return since it's likely controlled by aliens, especially when records showed that thousands died under the comet's orbit via spontaneous combustion after a strike of lightning, leaving nothing but bones, and this phenomenon is still occurring. Norby also explained that, because the comet followed no natural laws, it could return again, as it might have merely been observing Earth like a satellite, and that there was no better explanation, with nobody being humanly capable of disproving it.
6 years later on August, Norby and Hue descended the observatory after photographing a new star in the Antares cluster with a new telescope. But they came across a sentient fireball of the same color as the comet in a tree. They observed in horror as the new creature consumed people in fire with fingers of lightning. This creature tried to attack Norby and Hue until they concealed themselves in the observatory. The two realized that these creatures are predatory lightning and fire that arrived to Earth from Norby's Comet, and the new star in the Antares cluster is the comet planning it's next move. The two stayed in the observatory for their safety all afternoon, as they watched in horror on the news that all the Fire Vampires were killing people around the world, arriving through electric bolts of lightning, and nobody could escape via air or sea.
Later that night, in the Atlantic coast, the comet returned and Norby and Hue heard of it appearing first in China. The comet formed mile-long fiery letters in the sky spelling a message, in different appropriate languages over each country:
"People of Earth, you are ours by right of conquest. Hence forth and forever you belong to us, of Ktynga, known to you as Norby's Comet. You cannot fight us, nor defeat us, nor evade us. We are superior to you in every way. At irregular intervals, we shall return and claim as our due from 20-50 thousand of your inhabitants. We desire nothing else. But we insist upon the payment, and we shall take it. If you resist, we shall take more. On our next visit, we shall claim John Hanby, the president of the Federated Nations, Axel Gruno, master scientist of the world, Sin Lo Hoi, commander-in-chief of the International Army, Gustav Norby, of the Mount Wilson Observatory. These men must place themselves in the evening of August 27th, 2332, at the peak of Mount Wilson. If they are not there, we shall take 100 thousand lives instead of 20. Fthaggua, Lord of Ktynga."
Hue was horrified, convinced this is a hoax, and recommended fighting, but Norby claims that there's nothing they can do for the moment and that they had five years to prepare, as these creatures, Fire Vampires as he describes them, are pure energy and cannot be opposed easily. They even fed on heart, mind, and soul so that they may gather knowledge, memories, and so on last time they arrived, so that they could communicate with them now. But he believes that they fear him because he poses a threat to them for warning of the dangers beforehand, and claims he needs Hue's help to prepare for their arrival in the next five years.
Five years later, the people feared for the impending arrival, and plans to prepare have failed. Norby was planning to have the specified three people arrive to fulfill Fthaggua's request except him, whom they will perceive to be dead, with Hue skeptical that if this fails, 100 thousand will die. But when they hid behind curtains and were caught by a Fire Vampire posing as a human, 100 thousand died immediately. Hanby, Gruno, and Hoi were taken, and another message was given that they would be back in July 17th, 2339, threatening to wipe out all of America unless Norby was given. Angry, Norby and Hue tracked the comet's movement via their telescope and found that on it was a fortress with alien geometry. It was as big as a city and could hold thousands of Fire Vampires, and he felt that he could use the telescope to find a weakness. Soon he found it, but he refused to share it.
In the next five years, weapons were devised to harm the Fire Vampires, and massive evacuation orders to other planets, especially in America, were underway, and overpopulation caused pandemonium, protests, and intermittent warfare. But Norby had a secret plan to guarantee Fthaggua's defeat, even when he was branded a coward and traitor for causing 100 thousand deaths. Mount Wilson was a forbidden site by the government and yet Norby and Hue devised a plan to confront Fthaggua, with Norby knowing his weakness. On the specified date of July 27th, 2339, Norby stood inside a crater that used to be where the observatory was, as a detonation of several tons of dynamite made it look like a volcanic eruption. In the center of the crater was a large flat boulder, and the ends of the crater were lined to the top with irregular projections and ledges, Hue making his way to the biggest one at the base. He stood on the boulder and behind him was a labyrinth of machinery, including peculiar dynamos, and in front of him was an electrointerferometer to detect high electrical discharges and an important triple-switch, playing it carefully as one slip-up would mean the death of America. After hours of waiting, the comet finally arrived and Hue flickered the switch, sending Norby down a hidden trapdoor and the elaborate machine successfully imprisoned the attacking Fire Vampires. Then a chain reaction from continued use connected itself to Fthaggua, and a powerful discharge killed him and all the Fire Vampires on Earth, leaving the comet to orbit the planet.
In an interview with Norby, he said that Fthaggua was merely a unified organism of all the Fire Vampires which were merely living limbs for him, and thus if he was destroyed, so was all the Fire Vampires, and by using pure energy against a being of pure energy, it would be an effective weakness, all done only by guesswork, claiming that he couldn't help but feel respect for an entity that almost succeeded.