The series is written in a non-linear style: the principal narrative is frequently interrupted by flashbacks to events that occurred decades, or even centuries, before.
The kingdom of Deverry was founded by a fictional Gallic tribe that fled Gaul to escape Roman rule.
Also known as elves, the Westfolk physically resemble humans in most respects, although they can be distinguished by their pointed and furled ears, as well as their eyes which have catlike irises.
There is a second, smaller population of Westfolk dwelling on an island south of the Bardekian archipelago, and another far to the west of Annwn past their destroyed cities.
There are two different dwarven populations, both of which live in cities that are partially or primarily underground, and which make use of artificial and natural caves and tunnels.
Connected with the dwarves is a remote and sparsely populated city, Haen Marn, which travels through space and possibly time.
Some Guardians have great magical prowess, most notably Evandar who is responsible for bringing the original human settlers of Deverry from our world to Annwn.
Because one of their cultural practices is to eat the flesh of their own dead, the Horsekin were struck with a cholera-like plague which almost completely destroyed their population.
The term “Gel da’Thae” refers to civilized Horsekin that live in these settlements, while the term “Horsekin” in its stricter sense refers to the uncivilized tribes that dwell on the high plains north of the Rhiddaer, who have a culture extremely different from those living by the elven ruins, and who are considered barbarians by the city-dwelling Gel da’Thae.
Resembling the legendary creatures in European folklore and mythology, the dragons are enormous, four-legged reptiles with two batlike wings and long tails.
Those that follow the "dweomer of light" are servants of spiritual beings called Great Ones (analogous to the Buddhist concept of Bodhisattvas),[citation needed] and work to better the world in some way.
The past-life flashbacks deal with several of Nevyn's failed attempts to fulfill his oath and with the beginnings of the Time of Troubles, a decades-long period of civil war.
The fifth through eighth books are concerned with Rhodry's self-imposed exile and subsequent quest to find a dragon, and a Horsekin invasion of Deverry.
The ninth through eleventh books feature the Time of Troubles in the past and the Rhiddaer in the present, with consequences for an entire race.