In one sense, the central character is not any person (though some families are focused on, such as Yuli the Priest's line, which dominates Helliconia Spring) but the planet itself and its science, particularly in the light of James Lovelock's Gaia Hypothesis.
The books describe realistic and credible details of the planet from the perspectives of a great variety of fields of study – astronomy, geology, climatology, geobiology, microbiology, religion, society, and many others – for which Aldiss gained the help of many Oxford academics.
The Avernus was dispatched to monitor but not interfere with Helliconia, providing the Earth with scientific data and the entertainment of an epic reality show aired on a network of "eductainment".
Previously Helliconia only orbited Batalix, but the Helliconia-Batalix system was captured by Freyr's gravitational pull about eight million Earth-years ago[8] (i.e., very recently by astronomical and evolutionary standards).
This means that small-year seasons are harsher, but the planet still has huge polar ice caps, capable of surviving even the great summer, and the human-habitable surface area is comparable to that of Earth.
Although Helliconia appears to share many organisms in kind with Earth, the trilogy describes a variety of exclusive plants and animals, and how they cope with the extremes of the climate.
For example, in Summer, when temperatures are stifling, some plants are used decoratively (Scantiom -- hung for its appearance and cooling balm), recreationally (Veronikane -- set alight in a way similar to tobacco), or even for nourishment (Pellamountain -- infused in water to prepare a kind of tea).
Phagors, also called ancipitals (meaning "double-edged", in reference to their horns), are white-furred humanoid beings, roughly the size of humans but with features resembling the mythical minotaur.
Having evolved during Helliconia's earlier cold period, phagors are very different from humans in many ways: their blood is golden rather than red, their guts are located above their lungs, and they have an utterly alien intellect and psychology.
If a phagor reaches great age, it begins to shrink and gradually becomes keratinised, so that it eventually resembles a small totem showing no outward signs of life.
By the end of each great autumn, humans have developed levels of civilization comparable at their most advanced to Renaissance Europe, with technology such as telescopes, map-making, and porcelain glass.
Some rare people in remote areas are immune to the virus; these are considered ugly pariahs by the majority of the population, as they are horribly fat or thin compared to the prevailing standard.
Nonetheless, many inhabitants of Avernus choose to enter a lottery in which they can win the chance to visit the planet's surface and interact with the population, knowing that the deadly disease will kill them within a matter of days.
A striking difference between Earth-humans and Helliconian humans (and phagors) is the latter's ability to communicate with the spirits of the dead as their life force is slowly returned to the Original Beholder.
The "prelude", entitled Yuli, is set during the end of the Great Winter and follows the story of one man from youth into adulthood; this takes up about a quarter of the book.
This narrative traces the intertwined lives of many people and the changes in their society as the climate warms, setting these events within the overarching framework of the planet's natural cycles.
To their amazement, they discover a relatively advanced town called Embruddock, the remnant of what had been the capital of an empire during the previous Great Summer (although this history is long forgotten).
This place has the advantage of being situated in a geothermally active area, which has provided just enough warmth throughout the Great Winter that Embruddock has retained some fragments of its former culture (mainly in the skills and records of the craftsmens' guilds and in the stone towers).
Aoz Roon, a callous and unimaginative man, opposes this, only begrudgingly accepting it as Shay Tal unintentionally gains a reputation as a powerful sorceress.
As she continues her research into the history of Embruddock, and after communing with the souls of the dead, she discovers that during the hardest depths of the Great Winter, phagors ruled the area and enslaved humanity.
Shay Tal's main disciple, a woman named Vry, disagrees with this obsession with history and urges the academy to study the movements of the stars and think more about the future than the past.
Meanwhile, the residents of the space station Avernus are holding occasional lotteries to ameliorate their ennui, the winners being allowed to go down to Helliconia and experience a few short weeks of "real life" before succumbing to the Helliconian microbes (against which Earth humans have no immunity).
This novel focuses on the previously mentioned Campannlatian seaside settlement of Borlien, which has also grown into a powerful kingdom ruled by King JandolAnganol, who now agrees to divorce his beautiful wife, Queen MyrdemInggala, so he can wed the rather young Oldorandan princess Simoda Tal and secure a more favorable political alliance, as the nations of the planet's different continents have fallen into warfare.
The book tracks JandolAnganol's slow descent into madness through a temporally skewed perspective, and a series of flashbacks and flashforwards, showing him initially when he is about to divorce his wife, then moving back to the disastrous Battle of the Cosgatt, where his army had been defeated by firearm-wielding rebels.
He associates with the Madis (a nomadic subspecies of Helliconian human that communicates mainly through songs and chantings, and understands little of the passing of time), and finds his way to Oldorando (which now knows a climate similar to that of a rainforest).
Billy is a human man (of the Earth variety) from the space station Avernus, who wins one of the aforesaid lotteries and is permitted to spend some time down on the surface of Helliconia.
He hopes to meet the Queen MyrdemInggala, and as he begins to succumb to the Helliconian microbes (having no natural immunity against them), he imparts to some select natives a few truths about Helliconia and the universe at large.
The Wheel is an extraordinary revolving monastery/prison built into a ring-shaped tunnel with a single entrance and exit, powered entirely by the efforts of the prisoners pulling it along by means of chains set into the outer wall.
It is during this voyage that a great deal of information is discovered about the deep past of the Helliconia-Batalix solar system, its capture by Freyr, and the intertwined fates of humans and phagors.
A party is arranged to celebrate Luterin's freedom and also to observe the day of Myrkwyr, when Freyr is seen for the last time, marking the beginning of the centuries-long great winter.