Almuric is a planetary romance penned in the Burroughsian style. Its hero is Esau Cairn, an old-fashioned boxer hopelessly incompatible with the modern American society. When a crooked politician tricks him into complicity, Cairn is overcome with blind rage and thrashes the politician to death. Realizing there is no future for him on the planet Earth, Cairn asks help from a scientist friend, who teleports him to the recently-discovered alien planet of Almuric, a savage but habitable world in another universe.

Lone and naked, Cairn must gather and hunt his food and battle various bizarre animals. Eventually he stumbles upon the native people of Almuric, the Guras, who are hairy, ape-like men with a violent but pragmatic way of life. They live in great fortified cities and wage endless wars against each other, carbine and sword being their weapons of choice. Cairn begins to enjoy this new, simpler and truer existence, and his strength and fighting prowess earn him the nickname Ironhand.

The Gura women are not apish at all, but resemble human women; for the male Guras endure all hardships and evolved to be powerful and animalistic, while female Guras are shielded from hardship and evolved to be soft and beautiful. Cairn falls in love with a beautiful Gura female Altha, whose temperament and worldview are the most human-like of all Guras. Yagas are a black-skinned race of winged men, and sempiternal enemies of the Guras. Every now and then they raid Gura cities in the search of new slaves to torture and cannibalize.

Cairn and Altha are captured by Yagas and taken to their "black citadel of Yugga, on the rock Yuthla, by the river of Yogh, in the land of Yagg". The Yaga queen Yasmeena attempts to seduce Cairn, who declines and escapes. Discovering a secret tunnel unknown to most Yagas, Cairn returns to the Guras and persuades them to stop infighting and unites them against a common enemy. Cairn leads a combined army of Gura warriors to Yugga through the secret tunnel, taking the Yagas by surprise.

Seeing her people defeated, Yasmeena unleashes "the ultimate horror", a monstrous slug with dozens of spark-emitting and flame-flashing tentacles, but Cairn manages to defeat the abomination. The surviving Gura warriors, as well as 50,000 freed slave-women, return to the Gura homeland. Cairn takes Altha as his wife. The two decide to do what they can to pacify the quarrelsome Gura, making life on Almuric somewhat more civilized.