This is a timeline of events as they take place in the fiction of American horror author H. P. Lovecraft.
- George Gammell Angell, Professor Emeritus of Semitic languages at Brown University, is born.Cite error: Closing </ref> missing for <ref> tag.
- William Channing Webb encounters a "singular tribe or cult of degenerate Esquimaux" on the western coast of Greenland. This caste is found repeating the chant "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn."
- A meteorite falls in a small farming community west of Arkham, Massachusetts, on the property of Nahum Gardner. Professors from Miskatonic examine a piece of the meteorite and are baffled by its properties.
- During harvest season, Nahum deduces that while his crops have grown to a phenomenal size, the meteorite has poisoned the soil of his land, causing his harvests not to ripen properly.
- The McGregor boys of Mountain Hill discover a horribly distorted woodchuck while hunting on the Gardners' property. This is only one of numerous cases of animals on the family's land which behave unordinarily.
- Abnormally sized skunk-cabbages begin to sprout in Nahum's crops, sporting unknown color and a foul odor.
- The bizarre phenomena surrounding the vegetation on Nahum Gardner's property becomes unbearable for the country folk, leading to the abandoment of the road past the Gardner home.
- Nabby Gardner is the second member of her family, after her son Thaddeus, to notice the branches of trees beyond her home are swaying without the aid of wind.
- A windmill salesman from Bolton reports to the Arkham Gazette that during his travels he took notice to the Gardner property and the fact that the vegetation on the land emits a "distinct luminosity" in the moonlight.
- Toward the end of May, the cows on the Gardner property begin to produce bad milk. Nahum has the herd relocated upland, after which the problem ceases. At this point, it also becomes apparent that the vegetation on the Gardners' land is graying.
- Around the first anniversary of the meteorite's landing on Nahum Gardner's land, Nabby, the farmer's wife, is driven insane. Nahum opts not to send her to the country asylum, instead letting her roam about the house so long as she isn't a harm to the family. However "[...] when the boys grew afraid of her, and Thaddeus nearly fainted at the way she made faces at him," Nahum decided to have his wife locked in a room in the attic.
- Nahum Gardner's mad wife ceases to speak, and begins to crawl "on all fours" and emit luminosity in the dark, as does the plant life on the family property.
- The graying vegetation on the Gardners' land begins to crumble, and the mad Nabby Gardner breaks her silence with "spells of terrific screaming."
- Ammi Pierce, a friend of the Gardner family, discovers the water being pumped from the family's well "was no longer good. It had an evil taste that was not exactly fetid nor exactly salty."
- Nahum's son, Thaddeus, goes insane after an encounter with "the moving colours [beneath the family well]." Like his mother, Thaddeus is left to roam the house until he becomes delirious, at which point Nahum relocates him to a room in the attic.
- On the Nahum farm, poultry begin to turn grayish and die and hogs grow abnormally fat before becoming brittle and crumbling like the property's vegetation. A similar phenomena affects the cows, whose bodies "would be uncannily shrivelled or compressed, and atrocious collapses or disintegrations were common." By the time of harvest, every animal which belongs to the Gardners has either died or fled the premises.
- On October 19, Thaddeus Gardner dies of the same affliction which claimed the Gardner family's vegetation and livestock.
- On the evening of October 22, Merwin Gardner disappears after going to the family well to pump water. The next morning there is discovered "a crushed and apparently somewhat melted mass of iron which had certainly been the lantern; while a bent handle and twisted iron hoops beside it, both half-fused, seemed to hint at the remnants of the pail." His remains are discovered the following month at the bottom of the well.
- Ammi Pierce visits the Gardner home where he finds Nahum Gardner has gone mad and his son Zenas has disappeared, with Nahum stating only that the lost boy "lives in the well."
- During the same visit, Pierce murders what he reveals to be a gruesomely distorted monster , or what Nahum´s wife has become,in the attic, and upon returning to ground level, finds Nahum "horribly brittle" and "distorted". Nahum's final words describe the entity which claimed him as "a kind of smoke" living in the family well, which must have traveled to Earth on the meteorite that impacted nearby 17 months prior.
- Pierce, accompanied by three officers, a coroner, a medical examiner and the veterinary who had treated Nahum Gardner's diseased animals, investigate the Gardner home. They find the remains of the farmer's sons Merwin and Zenas at the bottom of the well. Later that evening, the seven men witness the smoke described by Nahum extract a similar color "tipping each bough like the fire of St. Elmo or the flames that come down on the apostles' heads at Pentecos," and they flee the scene before the smoke being darts into the sky and the Gardner property erupts a "cataclysm of unnatural sparks and substance."
- On November 1, denizens of lagoon country in New Orleans seek the help of law enforcement in locating their kidnapped women and children. Twenty officers, led by inspector John Raymond Legrasse enter the woods with a squatter from the swamp as their guide, where they proceed until they come upon a gathering of 54 voodoo cultists who also chant the phrase "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn." Of the 54 cultists, five are killed in the ensuing firefight and 47 are apprehended, with two severely injured. The most notable prisoner is Castro, who reveals the history of the Great Old Ones.
- Angell is first exposed to the Cthulhu cult, when Legrasse attends the American Archaeological Society's annual meeting seeking expertise on an idol recovered from the forest of Louisiana. It is here that both Legrasse and Webb publicly reveal their encounters with Cthulhu cultists.
- A Boston surveyor visits Arkham, Massachusetts and a countryside to its west, which is to be flooded for a new reservoir. Here, he meets with farmer Ammi Pierce, who explains the gruesome tale surrounding his friend Nahum Gardner's land forty years prior. In light of Pierce's recollection, the surveyor returns to Boston to give up his position and vow never to drink the water of Arkham after the flooding of the "blasted heath."
- On February 28, a large proportion of artists around the globe begin dreaming of "bizarre" things involving the Great Old One Cthulhu, and his city of R'lyeh beneath the Pacific Ocean. Earthquakes also occur throughout the world on this date, according to the International Date Line.
- On March 1, art student Henry Anthony Wilcox contacts Angell, bearing a clay bas-relief he sculpted using a recurring image in his dreams, asking the professor's advice in identifying the hieroglyphs on the statue. This begins Angell's studies of Wilcox's dreams, culminating with a document he entitles Dream and Dream Work. Also on this date, a great storm occurs and throws the Emma considerably southward off-course, and earthquakes occur throughout the world (although the International Date Line asserts that these tremors took place on the preceding day).
- On March 22, the Emma encounters the heavily armored steam yacht Alert, who orders the schooner to turn back. Captain Collins of the Emma refuses, leading the Alert to fire upon the Emma using a brass cannon. In retaliation, the crew of the Emma manage to board the Alert and slay all of its members, although Collins and First Mate Green are killed in the battle, leaving Second Mate Gustaf Johansen in command of the crew. Out of curiosity, the Alert proceeds in the original direction taken by its slain crew.
- On the night between March 22 and 23, "hysterical Levantines" mob policemen in New York.
- On March 23, Wilcox did not attend his daily meeting with Angell. Angell learns that this is because he has "been stricken with an obscure sort of fever" and has been placed into the care of his family. Angell's nephew, Francis Wayland Thurston, later learns from Angell's manuscript that "[Wilcox] had cried out in the night, arousing several other artists in the building, and had manifested since then only alternations of unconsciousness and delirium." The instances of dreams involving R'lyeh also become more intense, to the extent of giving the dreamer delirium. Thurston does research of his own, and discovers in Norway that on this date, the crew of the Emma (now manning the seized Alert) arrive on the shores of an uncharted island, characterized by the oozing stone architecture seen in the dreams of Wilcox and countless other artists of the world. The men come upon an acre-great portal compared in Johansen's manuscript to a large barn door, which their investigation manages to open. From it appears Cthulhu, who immediately slays three men. Two others Johansen presumes "perished of pure fright in that accursed instant," while another was "swallowed up by [...] an angle which was acute, but behaved as if it were obtuse." Only Johansen and William Briden are able to escape the island, and when Cthulhu takes to the sea in chase, Johansen retaliates by ramming the boat into the deity's head, promptly bursting it. As Cthulhu regenerates, the Alert evacuates the scene.
- Towards the end of March, outbreaks of mania erupt throughout the world. A London man commits suicide in his sleep. A South American man sends "a rambling letter to the editor of a paper" where he "deduces a dire future from visions he has seen." A dispatch from California describes a theosophist colony as donning white robes en masse for some "glorious fulfillment" which never arrives, whilst voodoo orgies multiply in Haiti, and African outposts report ominous mutterings, among other happenings.
- On April 2, "exceptionally heavy storms and monster waves" cause the Vigilant to be driven considerably southward off-course for Sydney. Naturally, the Alert experiences this storm as well. The bizarre dreams of R'lyeh experienced by artists around the world also come to an end. Also at 3:00 P.M. on this day, "every trace of Wilcox's malady suddenly ceased" and he was left relatively unaware of the delirium he had been experiencing since the night of March 22. On April 5, Wilcox returns home, having been pronounced well by his physician.
- On April 12, the Vigilant sights a heavily armored steam yacht, the Alert, populated by two men, one of whom has been dead for more than one week.
- On April 18, the Sydney Bulletin announces Vigilant's discovery of the Alert.
- On November 23, at the age of 92, Angell dies suddenly after "a careless push" from a sailor "on a narrow hill street leading up from an ancient waterfront," while returning from the Newport boat. His research notes on the worldwide Cthulhu cult are discovered soon after his death by Thurston.