The Scarlet Citadel is one of Robert E. Howards original works about Conan. This article contains a summary of the content of The Scarlet Citadel. If you wish to read the story yourself, you can do so here.
The story takes place when Conan is king of Aquilonia. Conan rides to Ophir to aid his ally Amalrus, king of Ophir, against the invasion of Strabonus, king of Koth. When he arives in Ophir, Conan and his five thousand horsemen are met by the joint forces of Ophir and Koth, allied against Conan. Being outnumbered by far, Conans army is destroyed and Conan himself is captured. He is taken to The Scarlet Citadel, the home of Tsotha-lanti. He's given a choice to abdicate his throne, make Prince Arpello of Pellia the king of Aquilonia and his life will be spared. Conan refuses, and is chained in the Halls of Horror. Left to be eaten by Tsotha's giant python, Satha.
While chained in the Halls of Horror, a slave comes down to Conan with the keys to his shackles, revealing he had been chief of a tribe that Conan and his men killed when Conan was a pirate. Conan had killed the slave's brother, and wanted Conan dead. Right when the slave is about to kill Conan, Satha attacks the slave, throwing him accross the room. To Conan's luck, the sword and keys the slave had brought was knocked out of his hands when Satha attacked. Conan is able to reach the keys with his feet, managing to free himself.
When he attempts to get out, the grille that locks the Halls of Horror is shut right in his face by Shukeli. Conan strikes Shukeli with his sword through the bars, killing Shukeli, but finds out that the grille can only be opened from the outside. He goes further inside the halls, where he finds a man apparently being killed by some kind of plant. Conan cuts down the plant, freeing the captive from it's grip. He learns that the man is the Kothian wizard Pelias, who was captured by Tsotha ten years ago, and many thought to be dead.
Conan and Pelias walks to the grilles at the entrance to the Halls of Horror, where Shukeli's body lies outside. Pelias, using his magical powers, makes the body of Shukeli rise to open the grilles from the outside. Once outside their prision, Conan has to get back to Aquilonia to protect it from the invading forces of Ophir and Koth. Conan himself is unable to think of a way to get there quick enough, but Pelias calls a bat-like flying creature that transports Conan to Tamar.
Meanwhile in Tamar, word has reached the city that the king is dead. The people are panicing, and the mercenaries started looting the city. Count Trocero, left by Conan in charge of the city while he was gone, swept down on the looters, but this didn't help against the panic. Soon, Arpello convinced the council that he should be made king.
Conan returns to the city and kills Arpello. He gathers an army and marches towards Shamar which is under siege by the enemy. Even outnumbered, Conan defeated the Ophirs and Kothians, even though they were outnumbered, mostly due to their superior Bossonian archers. Conan makes his way to Amalrus and Strabonus, and kill each of them. Tsotha flees, and Conan follows him. Conan doesn't gain anything on Tsotha, their horses running at approixmately the same speed. Then a giant eagle comes down from the sky and attacks Tsotha's horse. Tsotha is thrown off his horse, and Conan and Tsotha fight, ending with Conan cutting Tsotha's head of. Even after Tsotha's head is separated from his body, Tsotha's body keeps moving, as if trying to find his head. The eagle sweeps down and pics up his head, while the headless body of Tsotha runs out into the desert.