After escaping from her previous employer, Valeria of the Red Brotherhood finds herself lost in a seemingly endless jungle. She's quickly joined by fellow deserter Conan, who is quite smitten with her, only for the two to be immediately attacked by a large dragon. Stranding them on a rocky outcrop, they see a field stretching out from the jungle, and further still, a domed city far away in the distance. Stabbing the dragon with a poisoned spear, they make a break for the clearing, eventually arriving at the city gates after a full days travel.
They find the city to be seemingly deserted, made up of a endless maze of emerald green alcoves and hallways, lighted by flaming green crystals. After much exploring, they stumble upon a terrified individual, and are immediately set upon by attackers using mysterious artifacts. After saving the man, he introduces himself as Techotl, and hurriedly brings them to his people, as there are things which hide in the dark hallways.
The leaders of his people, Olmec and Tascela, tell them the tale of their people; how their people separated into three factions decades ago and have been waging war ever since, how barely more than fifty of them still live, and how one of the factions was killed off, its leader Tolkemec gone mad to live in the catacombs beneath the city. Behind their throne sits a black pillar covered in red nails, each representing a slain enemy. They offer to help Conan and Valeria escape if they help them slay the last remaining members of their enemies, which they begrudgingly agree to.
After repelling a surprise attack from their enemies, Olmec declares the war over, their enemies all dead. He commands Conan and several of his men to go check the enemy base for survivors. Whilst there, Conan is betrayed by one of the men sent with him, who says he was told to kill Conan so Olmec could have Valeria as his slave. Olmec tries to take Valeria, but as she repels him, Tascela arrives and takes her for her own, leaving Olmec to die on a torture rack. Conan arrives just in time as Valeria is about to be sacrificed to Tascela's hunger.
Suddenly, from out of the darkness, Tolkemec appears and proceeds to shoot everyone in sight with his magic wand. Conan narrowly defeats the mad wizard, and Valeria kills Tascela. The two of them embrace, and proceed to leave the now dead city.
Howard was suffering from many real world problems when he wrote Red Nails, such as a messy break up with his then girlfriend and his mother's failing health putting an emotional strain on him, as well as an ongoing battle with depression and financial ruin, which may explain the more visceral nature and downer ending as compare to some of his other Conan tales.
Marvel Comics adapted the story in comic book form in issues 2 and 3 of the Savage Tales of Conan the Barbarian, with art by Barry Windsor-Smith. An animated-adaptation has been in Development Hell for years.
- Action Girl: Valeria shares with Belit the distinction of being one of the two female leads in the original Howard stories who could handle themselves in a fight.
- Amazon Chaser: Literally; Conan has been tracking Valeria for some time after she slew a man who insulted her and had to depart rather hastily. As his current employers or the available women weren't much to his taste, Conan decides to chase after her.
- Call-Back: During his conversation with Valeria, Conan brings up the fact that he has been a pirate leader, a chief of the kozaki, a chief of the Zuagir and a chief of the Afghulies.
- Call-Forward: When Valeria gets fed up with Conan bringing up all the jobs he has had over the years...Valeria: Is there anything you haven't been?
- Cycle of Revenge: The people of Xotalanca and Tecuhltli have been at war longer than any of the combatants have been alive, and they have no idea how to stop it anymore.
- Defrosting Ice Queen: In a way. Valeria is initially not receptive of Conan's affections, but by the end she begins to reciprocate them.
- Designated Girl Fight: In the final battle, Valeria is the one who kills the villainess.
- Dinosaurs Are Dragons: The Marvel Comics adaptation reinterprets the dragon as a Stegosaurus. Howard's original description definitely does not invoke the imagery of a stegosaurus, with its tusks, snake-like eyes, serrated neck and back spines and a scorpion-like spike-tipped tail. The original Weird Tales art depicts a proper monstrous beast.
- Famed in Story: Valeria "of the Red Brotherhood, whose deeds are celebrated in song and ballad wherever seafarers gather."
- In the Back: Conan forgets the need to protect against this.
- Jack Bauer Interrogation Technique: When Valeria awakens to find a serving girl attempting to drug her, she beats the girl to find out why.
- Liquid Assets: Tascela does this.
- Pirate Girl: Valeria.
- Psycho Lesbian: Tascela shows signs of being one of these.
- Puzzle Boss: Conan figures out (after many zapped natives perish) that Tolkemec's wand can only hit things caught between it and any metal surfaces (such as the altar or doors of the room).
- Recycled Premise: The plot, which sees Conan and a female companion come across a mostly-deserted city that is being destroyed from within, bears some similarities to the earlier "Xuthal of the Dusk."
- Remember the New Guy?: As is typical for Conan stories, Valeria is an acquaintance of Conan's who was not established or referenced to in any previous story.
- Snakes Are Sinister: The crawler is a giant, ambiguously-colored snake that the people of Xotalanc found in the old catacombs and trained as their killer. Conan fatally wounds it in a dark room, and its corpse is found later on.
- Super-Persistent Predator: The dragon.
- Technicolor Fire: Actually, it's the smoke that's green.
- They Have the Scent!: The dragon. Even after it is blinded it is still able to pursue Conan and Valeria out of the forest on scent alone.
- Vain Sorceress: Tascela.
- Was Once a Man: Tolkemec.