The Scarlet Citadel

"The Scarlet Citadel" is a Conan the Barbarian story written by Robert E. Howard. First published in January, 1933.

King Conan is captured in a deadly trap by King Strabonus of Koth, his former ally King Amalrus of Ophir, and their evil sorcerous advisor (and true power behind the throne) Tsotha-Lanti. They want him to abdicate his throne in exchange for a pile of gold so that they can annex Aquilonia as part of their growing empire. Conan, being Conan, isn't having this one bit, and tells them all to go to hell. Tsotha pens him in the dungeons of the Scarlet Citadel, intending to feed him to his gigantic snake known as Satha. Meanwhile, Conan's kingdom is in a bad way, and the people suffer under the rule of Arpello, the puppet king installed by Strabonus and Tsotha. Conan escapes his bonds when a slave's attempt to avenge his brother upon him gets him killed by Satha. After braving the Citadel's many horrors, Conan finds and frees Pelias, a sorcerer and rival of Tsotha, who summons a giant flying beast to take him to Shamar, the capital of Aquilonia, and take it back from Arpello. Having taken back the capital, Conan rides with his army to take down Tsotha's imperial forces, and in a furious battle, Strabonus, Amalrus and Tsotha are all slain.

Tropes used in The Scarlet Citadel include:

Abdicate the Throne: Conan is offered bribes to do this
Always a Bigger Fish: A man comes to murder Conan, and feeds the snake sent to kill Conan.
Big Badass Bird of Prey: One attacks Tsotha's horse.
Buy Them Off: Offered to Conan
Cavalry Betrayal: Inverted
The Chains of Commanding: Conan reflects how he learned this on the throne.
Child by Rape: Tsotha-Lanti's purported Backstory. Demonic rape at that
Death Trap: Tsotha's dungeons
Dude in Distress: Conan
The Empire: Trying to capture his kingdom
Evil-Detecting Dog: When Satha flees before the sight of Pelias, Conan is notably unsettled by his assertion that the snake "saw his naked soul."
Evil Laugh: Pelias. Even though he's on Conan's side
Evil Sorcerer: Tsotha-Lanti
Evil Tower of Ominousness: Tsotha's citadel
Fed to the Beast: Tsotha pens Conan in the dungeon of the Scarlet Citadel with the intent of feeding him to his gigantic snake, Satha.
Giant Flyer: Pelias uses one to get Conan to his kingdom
The Good, the Bad, and The Evil: Sort of. Pelias isn't outright bad but as a sorceror he still gives Conan the creeps. Tsotha-Lanti however is definitely evil.
Leonine Contract: While Conan is prisoner, one of Tsotha's slaves tries to wheedle promises from him for his freedom, before then revealing that he was the brother of a chief that Conan killed back in his pirate days, and that he will settle for nothing less than Conan's blood.
Made a Slave: Conan remembers the markets
Man-Eating Plant: In the dungeons
Noblewoman's Laugh: An Eldritch Abomination produces this
Offered the Crown: Arpello claims this
One-Handed Zweihander: Conan wields a broadsword thus
Powder Keg Crowd: Started by rumors of Conan's death
Pulling Themselves Together: Tsotha-Lanti can do this.
Puppet King: The villains intend to install one
Religion of Evil: Set worship
Revenge: The slave that tries to kill Conan wants him dead because he killed his brother back during his pirate days, when he was known as Amra the Lion. Pelias himself isn't too fond of Tsotha either, especially after he forced him to watch his apprentices get fed to the big-ass snake.
The Rival: Pelias and Tsotha have a big-time case of this.
Self-Made Man: Conan
Sole Survivor: After the treachery
Succession Crisis: Triggered by Conan's disappearance.
Swamps Are Evil: Where you get your Eye of Newt.
Torches and Pitchforks: Develops because of the new king.
Turncoat: Amalrus
Virgin Sacrifice: When Tsotha learns that Conan has returned and has freed his old rival Pelias, in a Villainous Breakdown moment, he promises Set the sacrifice of five hundred virgins of Shamar if he will grant them victory over Conan's forces. Even Strabonus is horrified.
We Meet Again: Conan uses it at the end
What Year Is This?: Pelias asks Conan this.