The Shadow Kingdom
by Robert E. Howard
The story starts shortly after Kull, a barbarian from Atlantis, has conquered Valusia and become its King. Kull is invited to a feast by the Pictish ambassador for Valusia, Ka-nu the Ancient. Despite the fact that the Picts are ancient enemies of the Atlanteans, Ka-nu confides in Kull and tells him to expect the arrival of Brule the Spear-Slayer around sunset.
In the early night, Brule climbs into Kull's bedroom, identifying himself with a "bracelet of gold representing a winged dragon coiled thrice, with three horns of ruby on the head" which had been shown to Kull at the feast. Brule explains that Kull's life is in danger and shows him a series of secret passages which riddle the palace. Soon, Kull sees that the guards outside his room are all unconscious and their bodies hidden, although they still seem to be on guard at the same time. A visit by Chief Councillor Tu, with exposition from Brule, reveals the truth as Tu attempts to assassinate the sleeping King but meets him awake and armed; it was, however, not the real Tu but a serpent man who had taken on his appearance.
Brule reveals that the Serpent Men, an ancient pre-human race who had founded Valusia but were almost extinct, rule from the shadows, using their Snake Cult religion and ability to disguise themselves with magic. They intended on replacing Kull with a disguised Serpent Man, just as they had done with his predecessors.
The next day, the Serpent Men again attempt to replace Kull. He and Brule are, through an illusion, tricked into a separate room instead of the real council, surrounded by Serpent Men disguised as the councillors. Kull realizes the trap in time, however, and the two barely defeat their opponents. Heading into the real Council Room, they see another Kull. The imposter Kull is killed by the real one, revealing the fake as a Serpent Man and also revealing the truth of the existence of Serpent Men in general. The story ends with Kull's oath to hunt and destroy the Serpent Men for good.
However, in "Delcardes Cat" Kull encounters what seems to be, though not explicitly, a community of serpent men living under a lake (like the nagas of Indian mythology, arguably the source of inspiration for the serpent men) close to his capital. There, he discovers their version of the conflict between serpent men and "true" men, learning that the same thing may look quite different from the other side of the square. Probably Kull did abandon his vow to destroy the serpent men after that. Quite clearly, the land that is Stygia in the days of Conan was the last stronghold of the serpent men, long after Kull. It was the conquerors coming from the east, perhaps ultimately ancient Mu, who destroyed the Serpent Men.