The story takes place in Providence, Rhode Island and revolves around the Church of Starry Wisdom. The cult uses an ancient artifact known as the "Shining Trapezohedron" to summon a terrible being from the depths of time and space.
The Shining Trapezohedron was discovered in Egyptian ruins, in a box of alien construction, by Professor Enoch Bowen before he returned to Providence, Rhode Island in 1844. Members of the Church of Starry Wisdom in Providence would awaken the Haunter of the Dark, an avatar of Nyarlathotep, by gazing into the glowing crystal. Summoned from the black gulfs of chaos, this being could show other worlds, other galaxies, and the secrets of arcane and paradoxical knowledge; but he demanded monstrous sacrifices, hinted at by disfigured skeletons that were later found in the church. The Haunter of the Dark was banished by light and could not cross a lighted area.
The Shining Trapezohedron is a window on all space and time. Described as a "crazily angled stone", it is unlikely to be a true trapezohedron because of the Old Ones' penchant for bizarre non-Euclidean angles. It was created on dark Yuggoth and brought to Earth by the Old Ones, where it was placed in its box aeons before the first human beings appeared. After the passing of the Old Ones, during the final stages of the lower Triassic period, the trapezohedron was salvaged from the ruins of their cyclopean cities by the serpent people of Valusia. Eventually, after the bloody extermination of the serpent people at the hands of the advancing pre-human hordes of Lomar, the device found its way into the possession of the primitive men of Lemuria, Atlantis and in later cycles the Pharaoh Nephren Ka of Egypt until at last it was unearthed and brought to New England.
After the death of Robert Blake, who came to grief after discovering the Shining Trapezohedron and deciphering texts about it from ancient evil cults, the artifact was removed from the black windowless steeple where it was found by a Dr. Dexter and thrown into the deepest channel of Narragansett Bay. It was expected to remain there, under the eternal light of the stars, forever; yet, Robert Bloch's sequel, "The Shadow from the Steeple", proved that Nyarlathotep had cheated Dexter, forcing him to peer into the stone and throw the stone into the bay, where the eternal darkness of the depths gave the Haunter the power to remain perpetually free; it used this power to merge with Dr. Dexter and make him one of the world's leading nuclear scientists-in charge of atomic investigation for warfare.
Nyarlathotep appears in this story as the "three-lobed burning eye", a huge bat-winged creature, with a burning tri-lobed eye appearing unseen from the Trapezohedron. Blake realizes the horror can only travel in the dark. When a storm and power blackout envelop the city, he scribbles down his findings, concluding the story with his terrified record of what he can only glimpse of the approaching beast. "I see it-- coming here-- hell-wind-- titan-blur-- black wings-- Yog-Sothoth save me-- the three-lobed burning eye..."