The Saga of Pliocene Exile is a series of science / speculative fiction books by Julian May, first published in the early 1980s. It consists of four books: The Many Coloured Land, The Golden Torc, The Non-Born King and The Adversary.
However, the reality is far removed from the dream. The time-travellers arrive to discover the Pliocene is already inhabited by a dimorphic race of aliens ('exotics'). The exotics, who have fled their home galaxy because of religious persecution, are marooned on Pliocene Earth as well. The exotics have difficulty reproducing on Earth, and so have enslaved many of the humans in an effort to overcome this problem, interbreeding with the more robust humans.
Understandably, relationships between the exotics and the humans tend to be somewhat strained, and are complicated further by the exotics' metapsychic powers.
The exotics are known as the 'Tanu' and the 'Firvulag', and together constitute a single dimorphic race. The Firvulag are the 'metapsychically operant' [see below] members of that race, and the Tanu are the 'metapsychically latent' half. However, the majority of Firvulag have only weak mental powers, whereas the Tanu wear torcs, which are also mind-amplifying devices to allow use of their mental powers. The Tanu are generally much longer lived than the Firvulag. The four books of the Saga of Pilocene Exile abound with Tanu who are more than a thousand years old, who were not born on Earth, and who are called 'first comers' because of the fact. Examples of 'first comers' include King Thagdal, Celadeyr of Afaliah, and Dionket Lord-Healer. 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.
Tanu and Firvulag are sworn enemies, with each race routinely attacking the other. The only exceptions to this are in the month before and the month after the ritual Grand Combat, a gladiatorial combat that pits the Tanu against Firvulag. These two months are called The Truce.
Firvulag babies are frequently born to Tanu mothers carrying recessive Firvulag genes. These babies are cared for until they can be handed safely over to the Firvulag. Firvulag never produce Tanu babies.
Both Tanu and Firvulag can be killed by objects made of iron, which they call "blood-metal." Its use in weapons is forbidden by their battle code. Since the exotics are otherwise extremely difficult to kill, some humans take advantage of this weakness.
In the forty years before the start of the first book in the series, however, the Tanu have claimed ascendancy. Their use of humans to assist their reproductive capacity means that their numbers are rising, albeit with Tanu/human hybrids rather than true Tanu. This gives them an advantage in the Grand Combat (the annual ritual war between Tanu and Firvulag), since their human subjects and "half-breeds" fight on their side. The Tanu have won the Combat without fail for the past forty years, because of their use of grey-torc humans [see below] to fight the Firvulag, and other human innovations, such as the use of horse-like chalicotheres (known as 'chalikos') as riding animals (which gives the Tanu cavalry that the Firvulag lack).
There are some differences between pure Tanu and hybrids. Hybrids tend to be hairier, darker, have coarser features and less of the ethereal beauty of the Tanu. They also have a much more muscular figure, and often have stronger metapsychic powers. Unlike the Firvulag and the Tanu, hybrids are not poisoned by iron.
The Firvulag are primarily creative adepts, spinning horrific illusions around themselves in battle to terrify their opponents. They are merciless opponents and when working together are capable of driving a human or weak Tanu mind completely mad with their illusions.
The Firvulag martial tradition is very conservative. They do not ride chalikos into battle, unlike the Tanu and their human cavalry. They wear obsidian armor and fight using obsidian bladed swords and obsidian tipped spears. In battle, they fight like an unorganized mob of infantry. They usually throw their spears in the first rush of battle, then close in using their swords and mindpowers. For the last 40 years, the Firvulag have lost every single one of the grand combats because their unorganized and undisciplined infantry cannot withstand the shock of a heavy cavalry attack. Exiled humans introduced the concept of heavy cavalry to the Tanu and helped them mentally tame the chalikos.
Because of the constant defeats, the Firvulag have been recently growing desperate, and have been willing to take on lowlife humans like Madame Guderian as military advisors. The Firvulag are beginning to adapt more and more of human military tactics and equipment.
Technically they are ruled by the King of the Firvulag, but this is in name only, and they have their own king, Sugoll. Both by Sugoll's own assertion and the attestation of the rest of the Howlers, Sugoll is first among the Howlers in all things - mental power, physical ability, and, most of all, physical deformity. Sugoll, although often robed in an illusory body, is the most hideous and frightening of all the Howlers.
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. Interbreeding with humans, to revitalize their genetic stock with uncorrupted alleles, is a major component of this scheme, formulated by a slightly insane gold-torc human named Greg-Donnet Genetics Master (born Gregory Prentice Brown, M.D., Ph.D., D.Sc., L.H.D.), who had fled the Tanu capital of Muriah. Although the Howlers can create beautiful illusions around themselves to disguise their mutations, these illusions do not work on normal Firvulag. They are very effective for humans, though, which is fortunate for Greg-Donnet's schemes.
Some humans are happy with Tanu rule. Humans with valuable talents like genetics, robotics, etc. are often given golden torcs and are sometimes even ennobled. Other humans with great metaphysical powers are also given silver or golden torcs and may eventually achieve high rank. This is of course, as long as these humans are willing to work for the benefit of the Tanu. 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. For example, grey torc humans are used as shock troops, cavalry, cannon fodder, and as guards.
In order to increase their population more rapidly, the Tanu had been using humans as breeding stock ever since they arrived. The human women had their tubal ligation reversed. Those human women who are metaphysically gifted or have some unique, highly desired talent are often married off to Tanu nobles, after they each have had one night with King Thagdal. Thagdal is very fertile (which is the main reason he is king) so many women who are forced to sleep with him get impregnated. Those human women who are less talented but are beautiful end up in houses of pleasure where they are forced to service the sexual needs of Tanu. Any children resulting from this sexual slavery are separated from their mothers at birth and are placed in adoption with a Tanu couple, to be raised as Tanu.
Human males are also forced to become genetic donors. Those humans who are metaphysically or aesthetically gifted are approached by Tanu women who desire to have children. The human males are not allowed to refuse the sexual attentions of the Tanu. Some human men, however, find this duty not onerous as the Tanu ladies are often quite beautiful, exotic, and metaphysically gifted. Others quickly become burnt out, due to repeated metapsychic trauma.
Operancy: Psychic powers which are available for conscious, controlled use by a person. Basically, one is considered operant if they have psychic abilities and can consciously use them. In the Pliocene Epoch, the Firvulag were naturally operant. They did not require torcs or other mechanical assistance to be able to use their psychic powers.
Operant humans in the Galactic Milieu are not allowed to enter Exile, so most humans in the Pliocene are latent at most. The few who are operant are sometimes categorized using terms from the Milieu. These categories include master class (a well above standard amount of metapsychic powers ), the grand master class adepts (large amounts of metapsychic abilities, like Elizabeth), and the Paramount Grand Masters (enormous amounts of metapsychic power, including Marc Remillard, Aiken Drum, and Felice Landry). Individuals generally have different levels of ability in the various classes of metapsychic powers. For instance, Felice Landry is Paramount in creativity but only roughly masterclass in redaction.
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 theory, all humans have some psychic abilities, even though they may be hopelessly latent or extremely meager. The Tanu and the vast majority of humans are latents, with most humans having extremely meager abilities. The Tanu use torcs to allow them to use their psychic powers.
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. For example, Felice (an individual with extremely powerful latencies) has a natural ability to control animals, and many individuals with latent Creative powers are gifted artists or scientists, while those with latent Coercive ability may have substantial charisma - animal magnetism.
Creativity: the ability to create illusions, change shape and manipulate energy. The Firvulag are described as being naturally gifted at creativity, often using it to assume monstrous forms. More powerful individuals could use it to throw lightning bolts and so forth.
Coercion: the ability of metapsychic mind control over other people.
Psychokinesis: (or PK) the ability to move physical objects through space metapsychically. The most powerful PK Tanu used this ability to levitate a number of Tanu and their chaliko steeds as a Pliocene Wild Hunt.
Farsensing: the ability to communicate with others and to sense remotely via metapsychic means. Analogous to telepathy, clairvoyance and remote viewing. In the story "Intervention", this ability is initially termed ultrasensing.
Redaction: the ability of psychic healing and, to a certain extent, mind reading. This is most commonly described in the books for mental or psychological healing, but it is also used for healing physical ailments as well. It was also used in the Galactic Milieu to help latent metapsychics achieve operancy. It could also occasionally be used for interrogation and torture. In the Galactic Milieu recidivist criminals would be adjusted with this power.
Each latent or operant individual has a different combination of these abilities and, amongst the Tanu, those with similar abilities were organised into guilds, called the Five Guilds Mental, each with a guild leader. As of the start of the first novel, "The Many Colored Land", the leaders of the five Tanu guilds were as follows: the Coercer Guild was led by the human Sebi-Gomnol. The Creator Guild followed Aluteyn Craftsmaster, while the Farsensor Guild was led by Mayvar Kingmaker. The Psychokinetic Guild followed highly influential Nodonn Battlemaster (leader of the Wild Hunt), and the Redactor Guild was led by peaceful Dionket, Lord Healer. All of the guilds came under the authority of a Tanu noble called the Dean of Guilds, Lady Eadone Sciencemaster (the oldest surviving child of the Tanu King Thagdal).
A sixth power, prolepsis, is alluded to in The Saga of Pliocene Exile and explored a little in the Galactic Milieu trilogy. May does not clarify whether prolepsis, the ability to predict future events, is a separate metapsychic ability or merely a manifestation of extremely developed farsensory ability.
Dr. Eusebio Gomez-Nolan, a human who was given the name Sebi-Gomnol by the Tanu, invented the silver and grey torcs, along with much simplified torc-like devices for controlling the ramapithecine apes which do the drudge work in Tanu society. These lesser torcs allow for control of the wearer by any gold torc wearer.
Silver Torcs give operancy equal to that of the gold, but unlike the gold torc they also incorporate control circuitry. This allows a gold torc wearer to compel obedience in the silver torc wearer, allows for punishment or reward of the silver torc wearer via so-called pleasure-pain circuitry, and act as a means of mentally tracking the wearer. (Therefore a silver torc wearer can never succeed in running away, unless their metaphysical talent is so great it burns out the torc circuitry (see Aiken)). Humans with significant latent powers who come through the time-gate are initially given silver torcs. This allows the Tanu a degree of control over them until they prove themselves trustworthy, at which point they may be given a gold torc.
Grey Torcs don't enhance metapsychic powers at all, although they do grant the wearer a much simplified version of Farspeech. They have control circuitry like that found in the silver torcs. They are given to humans with no significant latent metapsychic powers at all, but who have skills which the Tanu consider to be vital or sensitive, e.g. physicians, technicians, soldiers/guards.