The books mainly concern the doings of the "Horseclans", a nomadic people originating from the "Sea of Grass"—the Great Plains from present-day southern Canada to central Texas, and from the Mississippi River to the Rocky Mountains, post-apocalyptically. The Horseclansmen were portrayed as fierce, noble and often gifted with telepathy, which came in handy for their dealings with their horses and "cats"—sabertoothed tigers that had been revived by scientific means in the years before the nuclear war.
Some people, including the Horseclans' founder and mentor-figure, Milo Morai, were "Undying"—effectively immortal or at least unaging and almost impossible to kill by means other than suffocation, drowning and decapitation. The Undying were also sterile, which was a source of anguish for some of them.
The known Undying were:
- Milo (who did not know his own age due to amnesia caused by a head wound in 1936),
- Bookermann (once a German cavalry officer),
- Mara (an Ehleen noblewoman who marries Milo),
- Aldora (an orphaned Ehleen girl taken in by one of the Horseclans),
- Demetrios (the Ehleen High Lord and the only Undying to perish during the course of the books),
- Drehkos (Nobleman of Morguhn involved in the Great Rebellion),
- Tim and Giliahna (the children of a Horseclans chief) and
- Neeka (an Ehleen physician who later also marries Milo).
In addition, Bookerman mentions two other Undying, one of whom he claims is dead.
Although not among the Undying, two other major characters are extremely long-lived, Hari Krooguh being almost two hundred years old when last mentioned in the books and Bili Morguhn, aka Bili the Axe, remaining active until his death from bear-inflicted injuries at the age of almost a century. In addition, both Hari and Bili possess extraordinarily strong mental powers of telekinesis and illusion (as does Aldora).
The Horseclans looked down on "dirtmen", or farmers, and by extension all non-nomads, although they later resettled on the east coast. Many "Dirtman" communities were descended from odd, out-of-the-mainstream groups of Americans, and often had religious beliefs that were unpleasant at best.
The main civilization in North America during most of the books is that of the "Ehleens"—a conglomeration of Greek-speaking Mediterranean peoples who had invaded the eastern half of North America and set up kingdoms. The main Ehleen kingdom, Kenooryos Ehlas (New Greece), was dominated by a thoroughly corrupt, debased version of the Greek Orthodox Church, and the conduct of whose rulers was, in some ways, also reminiscent of Hellenistic kings.
Other peoples the Horseclans dealt with were "Ganiks", "Mehrikans", and "Ahrmenee". The "Ganiks" were degraded descendants of hippie communes, whose religion of "Orghanikonservashun" (organic-conservation) forbade them to eat animal meat (but not human meat; Ganiks were enthusiastic cannibals), bathe, or hot-work metal (due to the pollution caused by burning coal).
In a similar fashion to the world of Robert E Howard's Conan and of Jack London novels, civilization is seen as having a softening and corrupting influence in comparison to the hardy Ahrmenee and the Horseclans, although not to the extent that they outweigh the peace and prosperity that Milo and others work towards.
The novels of the Horseclans series are the following:
- The Coming of the Horseclans (1975)
- Swords of the Horseclans (1976)
- Revenge of the Horseclans (1977)
- A Cat of Silvery Hue (1979)
- The Savage Mountains (1979)
- The Patrimony (1980)
- Horseclans Odyssey (1981)
- The Death of a Legend (1981)
- The Witch Goddess (1982)
- Bili the Axe (1982)
- Champion of the Last Battle (1983)
- A Woman of the Horseclans (1983)
- Horses of the North (1985)
- A Man Called Milo Morai (1986)
- The Memories of Milo Morai (1986)
- Trumpets of War (1987)
- Madman's Army (1987)
- The Clan of the Cats (1988)
In addition to the novels, there are two short story anthologies containing stories by both Robert Adams and others set in the Horseclans setting, Friends of the Horseclans, (1987) and Friends of the Horseclans 2 (1989)
The timeline of the series does not strictly follow the order of the series' publication, although there are times when the series sticks with the flow of the events for three or four books before going to another point in history. Several of the books consist mostly of flashbacks to earlier eras, including events prior to WWIII and even pre-WWII times. With few exceptions, no specific dates are given for events in the alternate history, although from time to time the author gives clues that allow reasonably certain dates to be calculated. The action appears to proceed along the following lines:
- 1980: WWIII. The aftermath, and dwindling of the remnants of civilization, continue for decades. Over the course of the next fifty years, Milo Morai develops the Horseclans people and leads them from being bomb-shelter refugees through a stage of subsistence farming, leading eventually to self-sufficient nomadism. Milo encounters Clarence Bookerman (Horses of the North).
- ~2030: Morai and Bookerman part, after a dispute over the merits of Nazism. Bookerman gives Morai advice that enables him to awaken his latent mental talents (Horses of the North). Bookerman wanders throughout the former United States, travels to Europe, and there, believing the former US eastern seaboard to be mostly uninhabited, initiates the two Ehleenee invasions.
- The Horseclans later encounter and ally with the prairiecats (The Clan of the Cats), and acquire the ability to communicate telepathically with their horses (Horses of the North).
- The Horseclans develop into their final plains-dwelling form. During this period the events of A Man Called Milo Morai, The Memories of Milo Morai, and A Woman of the Horseclans take place.
- ~2370: Morai leaves the clansmen in order to find a rumored settlement of Undying.
- ~2570: After two centuries of searching world-wide, Morai concludes that there is no community of Undying anywhere on earth. He returns to the Horseclans, and finding them living as he had left them, leads them on their prophesized migration to Ehlai (The Coming of the Horseclans).
- The clans cross the Mississippi river (Horseclans Odyssey).
- 2593: The political merging of the Horseclans with Kehnooryos Ehlas is completed, creating the Confederation (The Coming of the Horseclans).
- Blind Hari Krooger, tribal bard for decades, departs the Confederation to live again on the Sea of Grass. He takes many of the prairie cats with him. While travelling, he encounters the Teenehdjook, who overcome their customary distrust of humans and help him, and in turn he awakens their powerful mental abilities.
- ~2633: A Witchman, taking control of High Lord Zastros of the Southern Kingdom, leads a massive army against the Confederation. The army is defeated, Zastros and the Witchman controlling him are slain, and the dukes of the Southern Kingdom agree to join the Confederation. The rampant corruption of the Ehleenoee Church is laid bare, and the High Lord of the Confederation breaks up its control (Swords of the Horseclans).
- The dukes of the southern kingdom work to rebuild their duchies (Trumpets of War).
- Another Witchman, in the body of a young Ehleenee man, gains control of the aging commander of the Southern Kingdom army, and through him almost brings the duchies to revolt. The commander is slain and the Witchman is forced to return to the Witch Kingdom (Madman's Army).
- ~2949: The Great Ehleenee Rebellion: Witchmen infiltrate the Ehleenee Church and through it cause an uprising. The uprising is put down (Revenge of the Horseclans, A Cat of Silvery Hue, The Savage Mountains).
- ~2950: The Witchmen foment discord between the Ahrmehnee and the Confederation, prompting the latter to invade. After consulting the Silver Lady, the Nakharah (chief) of the Ahrmehnee learns that warring against the Confederation will result in the virtual extirpation of the Ahrmehnee race. He wisely merges the Ahrmehnee stahn with the Confederation. According to the Silver Lady, this happens about 12000 moons (~970 years) after WWIII (The Savage Mountains).
- Bili Morguhn and his mixed force of Confederation nobles and Freefighters, still in Ahrmehnee lands at the end of the brief war between the stahn and the Confederation, are cut off from the Confederation by a massive volcanic eruption caused by the Witchmen's meddling. They encounter and ally themselves with the Moon Maidens and some Ahrmehnee. They are then approached by the Kleesahks representing Prince Byruhn of New Kuhmbuhluhn, and soldier on his behalf, defeating bands of Muhkohee raiders and immigrating Skoshuhns. The Skoshuns and Kuhmbuhluners form a political union—a republic—with a Kleesahk as one of their chief advisors (The Death of a Legend, The Witch Goddess, Bili the Axe, Champion of the Last Battle).
- ~2980: The widow of the duke of Sanderz-Vawn tries to murder her stepson in order to have her son installed in his place. The plan is thwarted, and the stepson and his sister are found to be Undying (The Patrimony).
- ~3030: Bili Morguhn, Prince of Karaleenos, gets the bad end of an encounter with a bear while hunting. He lingers for several weeks, during which he re-lives the memories of his youth, and then dies (The Death of a Legend, The Witch Goddess, Bili the Axe, Champion of the Last Battle).
The original series, published by Signet, featured artwork by fantasy illustrator Ken Kelly. Part of the series was later published by Futura in the United Kingdom with new cover art by Luis Royo. Mundania Press are planning on re-publishing the entire series, the first of which (The Coming of the Horseclans) features artwork by Stacey L. King. At some point there were also covers done by Carl Lundgren of 60's psychedelic album-cover fame and Christos Achilleos for UK-only editions.
- http://www.kenkellyart.com/ Ken Kelly's artwork site
- http://www.luisroyo.com/ Luis Royo's official home page
- Horseclans series listing at the Internet Speculative Fiction Database
- http://www.mundania.com Re-publishing Robert Adams Work
- https://web.archive.org/web/20091027131304/http://geocities.com/evilsnack/horse.htm The Horseclans Project
- http://ofearna.us/books/adams.html (Franklin) Robert Adams at The BookShelf