Balthus is an young man, recently sent to help defend the border lands of western Aquilonia; lands which encroach upon the territory of the savage Picts. He meets and befriends Conan, a Cimmerian, who has been serving at the nearby fort as a tracker and soldier for several months. There have been a recent rash of murders, perpetrated by demonic minions of Zothar Sag, a Pictish chieftain.
Conan suggests breaking the shaky peace with the Picts in order to put a permanent end to the problem. He assembles a small team, including Balthus, who along with himself, will sneak into Zothar Sag's camp and kill him. However, this will require them to cross the Black River and into Pictish territory, a savage land for a savage people, populated by all manner of beasts, and some things out of their nightmares.
Often considered one of Robert E. Howard's greatest works, it features many of the recurring themes present in his other works, such as the man's innate barbarism and the impermanence of civilization, yet given far more focus here.
- A Boy and His X: Balthus and the dog, Slasher.
- Alone in a Crowd: Balthus feels alone in Conan's presence.
- Author Avatar: Balthus, according to Howard himself.
- Bring News Back: Conan and Balthus try to warn the Fort that the Picts are preparing a major attack. By the time they make the fort, it is fully besieged, so they make to warn Velitrium and the settlers in the path of the Picts.
- Deus Exit Machina: Conan and Balthus separate near the end of the story, mainly so Conan can have a fight with a forest demon while Balthus defends the escaping settlers in a Heroic Sacrifice.
- Distressed Dude: Balthus, one of the few male examples in a Conan story. He's captured by Pucts and Conan has to rescue him.
- Friend or Foe: Conan deludes a Pict by calling out in their language.
- Half-Human Hybrid: Zothar Sag is half demon-god, being a child of Jhebbal Sag, just like the swamp demon.
- Heroic Sacrifice: Balthus and Slasher Hold the Line while settlers flee the advancing Picts.
- Human Sacrifice: Part of the Ritual Magic used by Zothar Sag.
- Jungle Drums: The Picts use them to communicate, or just to threaten and terrify opponents.
- Libation for the Dead: Conan pours out a drink and smashes the tankard in respect for Balthus and Slasher.
- The Natives Are Restless: The Picts, not happy Aquilonia annexed some of their territory and fixing to do something about that.
- Panthera Awesome: A saber-toothed cat! Even Conan is shocked that one is still alive. Later an actual jaguar tracks the heroes through the forest.
- Power Glows: The forest demon, who glows with green fire.
- Ritual Magic: The Picts practice it.
- Scarily Competent Tracker: The Picts, to the point where despite traveling tens of miles through the forest, Conan tells Balthus it's only a matter of time until the Picts find them.
- Synchronization: Zothar Sag is a child of Jhebbal Sag, just like the swamp demon. The demon tells Conan that if one is injured, so is the other, and the ending confirms Zothar Sag died of wounds Conan inflicted on the demon.
- To Absent Friends: Conan and some woodsmen discuss the settlers and the people who died at the fort over drinks at the end of the story.
- Would Not Shoot a Civilian: Dead civilians enrage Balthus.