The rupture and the rapid filling of the Mediterranean, based on the geological event known as the Zanclean Flood, form a Wagnerian climax to The Golden Torc, in which aliens and time-traveling humans are caught up in this cataclysm.
Over time, both races (but especially the Tanu) were found to have difficulty reproducing on Earth due to the higher levels of terrestrial and solar radiation relative to their home world.
The plot follows a group of time travelers beginning with the events that caused them to seek exile from the future and the disruption they bring to the established societies in the Pliocene.
After the death of the inventor, his widow finds herself inundated with a steady stream of late 21st and early 22nd century misfits/outcasts begging to be allowed to escape the modern world for a chance to start over in the imagined simplicity of the Pliocene.
The widow finally gives in and eventually establishes a regular training program for the "groups" making the trip to ensure they have the basics for survival and a trade in the Pliocene era.
The exotics inhabiting the Pliocene Epoch, despite being separated from the appearance of humans on Earth by millions of years, closely resemble the Tuatha Dé Danann and Firbolg of Celtic Mythology.
The Firvulag are not usually as long lived, although they have a few first-comers of their own (King Yeochee and Palloll One-Eye among them), but are physically hardier and more resistant to Earthly radiation than the Tanu.
These two months are called The Truce and allow for trade between the two races and time to safely travel to and from the White Silver Plain or Field of Gold, depending on where the Grand Combat is hosted.
The Tanu (e.g., Nodonn Battlemaster, Kuhal Earthshaker, Minnanon the Heretic, et al.) are extremely tall, slim and beautiful, and live in large cities across southwest Europe.
Because the Tanu use humans to reproduce, a number of the 'Tanu' are in reality Tanu/human hybrids (e.g., Bleyn the Champion, Alberonn Mindeater, Katlinel the Darkeyed, et al.).
Because of their constant Grand Combat defeats, the Firvulag have recently been growing desperate, and have been willing to take on lowlife humans like Madame Guderian as military advisors.
After over-exposure to dangerous radiation in the radium-rich mountains they have chosen to live in, they have mutated into hideous, deformed entities, filled with self-loathing, who attack anyone who strays into their territory.
By the end of the series, the Howlers have left their radioactive mountain home and moved to the deserted Firvulag city of Nionel, where they set up a genetic plan to restore their hideously mutated selves to some degree of normality.
Thousands of years before the action of the novels, the inhabitants of Duat developed interstellar travel, and colonized other planets in their native galaxy.
The Firvulag who dwelt in the cold, high mountains close to the mines they worked for gems grew small and hardy and were naturally operant, but most were much more weakly powered and often limited to Creativity and Farsense.
Certain (female) members of Lene, known as Shipspouses, developed a symbiotic relationship with enormous sentient interstellar organisms known as Ships which were capable of superluminal travel.
She also has 2 legacy powers from her time as Shipspouse: the ability to D-jump and the "mitigator" program that greatly reduced the pain that traveling through the "gray limbo" of hyperspace causes to sentient races.
The daughter race intervened to prevent this, and so the remaining Tanu and Firvulag fled with the sympathetic Brede in her Ship into another Galaxy to survive or fight their Nightfall war to the end.
Earth was chosen as the best planet capable of supporting the lives of the two races that the Ship, now dying from the immense strain of the Intergalactic jump, could reach before its death.
Though ramapithecine apes are made to do a lot of the menial labor in the Tanu kingdom, human grey torc slaves end up doing the more complex and dangerous grunt work.
Those human women who are metapsychically gifted or have some unique, highly desired talent are often married off to Tanu nobles, after they each have spent one night with King Thagdal.
The only true "natives" in the book, the Ramapithecus are a race of small, somewhat fragile seeming hominids, believed (at the time of writing, though no longer) to be the original ancestors of modern humanity.
They are still heavily used in farming, mining and other forms of unskilled manual labour, and occasionally still used as surrogate wombs for Tanu offspring as was originally done before humanity arrived.
Humans in the late 21st century, along with the other races of the Galactic Milieu (the Lylmik, Gi, Krondaku, Poltroyans, and Simbiari) and the Tanu and Firvulag of the Pliocene epoch, have developed psychic powers.
Latency: Psychic powers which, although present, cannot be consciously used by a person – because of a lack of training, inhibiting factors, trauma, or mental blocks of uncertain origin.
In places May implies that individuals noted for possession of an extremely high level of a skill or an attribute are often latents who make unconscious use of their metapsychic powers.
Prolepsis, the ability to predict future events, is a sixth power alluded to in The Saga of Pliocene Exile and explored a little in the Galactic Milieu trilogy.
[3] May's studies in paleontology and climatology inform the Many Colored Land's geography, as well as helping readers to visualize the flora and fauna of the Pliocene epoch.
The presumption is that such myths and legends result from the peoples, individuals, and events in this story, creating a loop that connects the present to six million years in the past.
"[5] At the time of her death in 2017, Oscar-nominee Nick Dudman told Chicago Sun-Times writer Maureen O'Donnell that May's "...characters are wonderful, the sequencing is amazing, and the ideas behind the story are so bold" that he was developing her books for television.