The five stories that make up the cycle (in chronological order) are "The Dweller in the Tomb" (1971), "Out of the Ages" (1975), "The Horror in the Gallery" (1976), "The Thing in the Pit" (1980), and "The Winfield Heritance" (1981).
The cycle introduces various mythos elements, such as the Zanthu Tablets, the Ponape Scripture, Father Ubb and the yuggs, and two new Great Old Ones: Ythogtha and Zoth-Ommog.
The cycle also features the (fictional) Sanbourne Institute of Pacific Antiquities—perhaps Lin Carter's answer to Lovecraft's Miskatonic University.
Carter's "Demon Trinity" (Ghatanothoa, Ythogtha, and Zoth-Ommog) were spawned on a planet near the double star Xoth.
He is infamous for his horrid appearance, and fearsome medusa-like ability, which causes a viewer's skin to become hard and leathery but preserves the brain, leaving the victim to go slowly mad trapped within an immobile shell.
Ythogtha is the second son of Cthulhu and resembles a gigantic, humanoid frog, or Deep One, with only a single eye in the center of his forehead, like a cyclops.
He has a cone-shaped body, a razor-fanged reptilian head, like that of a Tyrannosaurus rex, four broad, flat, starfish-like arms with suckers, and a mane of tentacles.
It is based in Santiago, California and was founded by the son of the late Calton Sanborne II, whose father was a magnate in the tuna-packing industry.
One such statue is recovered from the seafloor of Ponape and brought to Professor Harold Hadley Copeland, a brilliant but eccentric archaeologist, who is researching the Xothic Legend Cycle.
After Professor Copeland dies in a psychiatric hospital, the statue is taken to the Sanbourne Institute of Pacific Antiquities to be displayed.
After killing the night watchman, the Deep One is about to take the statue when he is interrupted by Dr. Blaine's young aide, Arthur Wilcox Hodgkins.
As fate would have it, Hodgkins is charged with the murder of the night watchman, because the body of the Deep One had dissolved into a pool of slime and soon evaporated just a few hours later, leaving no trace, except for some badly charred clothing.
Hodgkins is judged incurably insane and is confined to the Dunhill Institute, where his mentor and close friend, Dr. Blaine, is also incarcerated.