Prior to the start of Section I, Lovecraft includes a preface that describes the text as excerpts from the papers of “the Late Francis Wayland Thurston, of Boston.” Lovecraft pairs this note about Thurston with a quotation from Algernon Blackwood, a famed writer of ghost stories, about the possible existence of epic and unimaginable creatures. When the story finally begins with Section I, “The Horror in Clay,” Thurston himself takes over as the narrator. He begins with the assertion that mankind’s inability to make sense of every aspect of the universe is a blessing. Thurston goes on to hint at a horrifying discovery that he once made by accident, emphasizing that he hopes no one else will uncover what he did. 

The story of Thurston’s revelation dates back to late 1926 when the papers of his deceased grand-uncle, Professor George Gammell Angell, arrive at his residence in Boston. Having been a scholar in Semitic Languages at Brown University, many sought him out with questions about ancient inscriptions. His death, Thurston explains, was mysterious, even puzzling doctors. Among Professor Angell’s belongings is a strange box that Thurston initially struggles to open. Once he locates the key, he opens the box only to find an even more bizarre object, a six-inch bas-relief made of clay, inside. The sculpture features an unrecognizable language and an image of a monster, complete with tentacles, scales, and wings. Thurston finds a note in Professor Angell’s handwriting that describes two different scenarios, both related to the mysterious Cthulhu Cult. 

The first narrative that appears in Professor Angell’s note details the strange experiences of a young man named Henry Anthony Wilcox. While Wilcox has a reputation for being eccentric, the clay bas-relief that he presents catches Professor Angell’s attention right away. Wilcox reveals that he created the sculpture in his sleep while he dreamed about “strange cities,” complete with gargantuan monoliths, green ooze, and the repeated sound of “Cthulhu fhtagn.” Professor Angell thoroughly questions him about any connections he may have to strange cults, but Wilcox has no knowledge of such things. He continues, however, to report back to Professor Angell about the dreams he has, many of which feature the sounds “Cthulhu” and “R’lyeh.” On March 23rd, Wilcox fails to appear for his scheduled interview, and Professor Angell learns that he has developed a strange fever. Barely conscious, Wilcox rambles to his doctor about a monstrous “thing” walking about that seems related to the image on his bas-relief. 

Almost as suddenly as it began, Wilcox’s fever disappears on April 2nd, and he cannot remember anything that he said or did during the period of his illness. Thurston explains that while Wilcox’s narrative ends there, Professor Angell interviewed many others about any dreams they may have had from March to early April. Most responses yielded nothing, but a collection of artists and writers each told of disturbing dreams that bore many similarities to Wilcox’s. Professor Angell also kept a series of newspaper articles from around the world detailing bizarre phenomena that occurred during the exact same timeframe as the reported dreams. After examining all of this evidence, Thurston believes that Wilcox knew of Professor Angell’s previous experiences with such strange happenings.