This combination fantasy/science fiction trilogy is about an enslaved planet, and a small group who intend to do something about it.
The Kelanni live in a medieval type of society, and are ruled by an unseen being called The Prophet. The Keltar are the Prophet's judge, jury and executioner. They go from village to village, kidnapping in broad daylight, and taking the unlucky ones on a one-way trip to "serve The Prophet." Their actual destination is much more brutal, and more down-to-earth.
Alondo is a genius who has had some Keltar training. Lyall is a musician who plays a very special type of instrument. Shann is an orphan child whose parents are "serving" the Prophet. They learn that the Prophet's skin is actually white, and his blood is red (the Kelanni have green skin and tails). They are joined by Keris, an ex-Keltar who brings along a strange being named Boxx, who has custody of an even stranger machine. It allows the group to speak to a woman from several thousand years in the past, who tells them of a weapon that will stop The Prophet, once and for all. Getting to the weapon is the hard part.
After many days travel, they reach the Barrier of Storms, which certainly lives up to its name. Their first attempt to cross is unsuccessful, because forces loyal to The Prophet are hot on their trail. They eventually cross in a modified sailing ship. Shann and Boxx are separated from the others, and find themselves in a much more technologically advanced society (the two societies know nothing about each other). Along the way, Shann and Boxx learn some really interesting things about themselves and their respective societies. Are they successful in stopping The Prophet, and un-slaving their world?
Here is an excellent piece of writing. The author does a fine job at making the Kelanni seem human, even though they are not human. It is very much worth the reader's time.