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 compared 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. Conan — Blood of the Serpent is a prequel to this story, showing us how Conan and Valeria first met.
- 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.
- Asshole Victim: The founders of the city were colonizers who enslaved the local black population to build it and then exterminated them when their magic made the slaves obsolete. When the ancestors of the Xochutl people showed up and killed them all, it was hardly undeserved.
- Attack Its Weak Point: Conan manages to take out the dragon by throwing an improvised poison javelin right into its gaping maw.
- Author Appeal: This story contains yet another scene of one woman stripping and flogging another, in this case Valeria interrogating the servant girl sent to drug her. Similar scenes showed up in Xuthal of the Dusk and A Witch Shall Be Born.
- Bear Trap: Conan rushes to stop the Human Sacrifice only to get caught in a foothold trap inset into the temple floor. He doesn't have his weapons with him so he can't even cut his leg off. Fortunately Tascela ends up releasing him in a last-ditch attempt to stop the mad priest from killing everyone.
- Big Labyrinthine Building: Xuchotl is an entire city built as a single, huge palace. Aside from the fortified citadels of the two warring factions, it's almost totally bare and deserted in the present day. When Conan and Valeria leave, there's very likely nothing alive in it at all.
- 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?
- Chickification: Much is made of Valeria's strength and skill with a blade, yet she's easily overpowered by Olmec and then Tascela (though it's implied Tascela's magic gives her Super-Strength) just so Conan can have a Damsel in Distress to rescue (no doubt so Howard can sell a story that matches the magazine cover). No wonder she kills Tascela just to get her self-respect back!
- Clothing Damage: Both Valeria and Conan have their clothes damaged in struggles near the end of the story, so both can display their impressive chests. Though Valeria's is impressive for a much different reason than Conan's.
- Conditioned to Accept Horror: The people of Xochutl have been isolated from the rest of the world and locked in an unending Cycle of Revenge for so long that they don't entertain any notion of ever living differently. Every single one of them is a fatalist who expects to die gruesomely at the hands of their enemy clan without ever seeing the outside world. Rather sadly, they're all proven right.
- Cruel and Unusual Death: The Tecuhltli and Xotalanca visit long, agonizing deaths on anybody they capture.
- Cycle of Revenge: The people of Xotalanc 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.
- Decapitation Presentation: In contrast to the titular red nails that the Tecuhltli use to mark their kills, the Xotalanca collect their enemies' severed heads in jars that are all displayed in their main hall.
- 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. The women of Xotalanc who attack Tecuhltli are also dispatched by Tecuhltli, not the heroes, and usually by Tecuhltli women.
- 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."
- Forever War: The war in Xuchotl has raged ceaselessly for 50 years and reduced both clans involved to mere dozens by the time our heroes arrive.
- Ghost City: There is not a single living soul in Xochutl after Conan and Valeria leave.
- Human Sacrifice: Olmec's ghastly evil is fully revealed when Conan deduces that he had kept the dragons in the forest satisfied by feeding his own people to them, and in turn used the threat of dragons to keep anyone from leaving the city. His wife Tascela does the same thing, ritualistically killing beautiful young women so she can use their essence to stay young forever.
- I Have You Now, My Pretty: Olmec kidnaps Valeria with the intention of raping her. Tascela shows up and steals Valeria from him before he can go through with it, locking Olmec in one of his own torture devices to add insult to injury.
- I Owe You My Life: Techotl is so grateful to Valeria and Conan for saving his life that he betrays his own prince to try and save them near the end. While he perishes for it, his efforts weren't in vain.
- In the Back: Conan's concern for Valeria's safety means he forgets caution in the presence of Olmec, leading Olmec to try a lethal unarmed strike at the back of Conan's head. Because Conan is Conan, he barely evades it.
- Jack Bauer Interrogation Technique: When Valeria awakens to find a serving girl attempting to drug her, she strips, beats, and whips the girl to find out why.
- Liquid Assets: How Tascela intends to drain Valeria's youth: with a kiss and a knife driven slowly into her heart, so Valeria's final breath will breathe vitality into Tascela.
- Male Might, Female Finesse: Conan and Valeria are about equally quick, but the narrator takes time to contrast Conan's overwhelming, savage ferocity with Valeria's skilled, dexterous fighting style.
- Our Dragons Are Different: The "dragon" fought by Conan in the jungle is not at all a Smaug-esque fire breathing flying creature, but a huge dinosaur with a crocodile-like head, spikes on its back, no wings, four ridiculously short paws, and a stinger on its tail.
- Pirate Girl: Valeria. Her taking a job in a landlocked army is odd enough Conan comments on it.
- Poisoned Weapons: Conan defeats the dragon by Macgyvering a javelin with some sticks and his poniard and then coating it in poison from one of the jungle fruits hanging nearby. One well-aimed throw into its gullet is all it takes to put the beast down, but not after a lengthy chase.
- Psycho Lesbian: Valeria gets vibes that Tascela is one of these. Turns out Tascela wants Valeria for even less savory purposes.
- 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. Conan — Blood of the Serpent is a prequel novel showing how they met.
- 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. Like a Graboid, when its prey is inaccessible it will just sit and wait until they become accessible or die of exposure.
- Technicolor Fire: The fire gems of the city give eerie green light, the floor radiates firey red, and the smoke of Tascela's ritual candles is 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.
- Throne Room Throwdown: The final battle takes place in Olmec's throne room.
- Token Heroic Orc: Techotl revels in violence against the Xotalanca just as much as the rest of his clan and comes off as deeply off-putting to Conan and Valeria, but he never betrays them out of gratitude for saving his life and he is eventually mortally wounded trying to stop Olmec from kidnapping Valeria. His dying act is to drag himself over to Conan and warn him about Olmec and Tascela's treachery, and his death is treated very somberly, with the narration noting how Conan and Valeria were the first people he had ever seen who weren't brainwashed by the crazed blood feuds of Xuchotl and how he had felt genuine warmth and camaraderie from them.
- Torture Technician: The people who originally built the city constructed many elaborate torture devices, which the Xochutl people inherited from them. It's apparently a cultural pastime for them by this point.
- Vain Sorceress: Tascela, consuming the youth of others to stay young and beautiful, and it's implied choosing the most beautiful women for this purpose because she has to be the hottest chick in the room.
- Villainous Rescue: Tascela shows up to stop Olmec from raping Valeria, exclusively so she can sacrifice Valeria and consume her soul. This is in turn stopped by the return of Tolkemec, who kills every mook in the throne room before she can consummate it.
- War Is Hell: Somewhat atypically for Howard, the war between Xotalanc and Tecuhltli is portrayed as an utterly pointless and savage Hopeless War with no glory and no heroes. Even Conan is unsettled by the bloodlust his temporary allies show and the tortures they relish in inflicting on their captives. Far from being an admirable Proud Warrior Race, the people of Xuchotl are portrayed as a pitiful and fearful people manipulated into a self-destructive blood feud by power crazed leaders.
- Was Once a Man: Tolkemec, devolved in the catacombs into something else. Not quite a full Frazetta Man, something definitely no longer human.