On one side of the River the Sun rules the sky and the Lao people live in eternal summer while on the nothern side the Moon holds sway over the cold forests of the Ugaro tribes. At the end of Tuyo, book one of the series, both peoples fought together to bring down an evil sorcerer. Because the epic battle took place in the Winterlands the Lao too injured to travel back to the River remained with the local tribe who promised to care for them. Surgeon Dedicat Suelen decides he must go and save those soldiers from the healing of ignorant savages. Everyone tries to dissuade him. Surviving in the Winterlands is almost impossible for a young Lao, and Suelen is in his eighth decade. He doesn't speak the language and knows nothing of Ugaro customs. Worst of all he is a Dedicat, one who uses magic to heal and the Ugaro consider all magic to be sorcery and a death sentence. But as a Dedicat he has sworn to heal all those in need and believes he go even if it means his death.

The plot is relatively simple. Suelen travels into the Winterlands, begins his work healing, eventually makes a mistake, and must defend himself and his methods. As with all of the Tuyo series it is the worldbuilding that is so exceptional and in Suelen the characters explore the true nature of their different magics and customs. Among the Lao most are born with the ability to cast small cantrips which are considered completely different from the mental magics of sorcery. The power of the Dedicats comes from performing invocation rituals to the Sun and using the Sun's power to heal similarly to the way Ugaro Singers ask the Moon to provide aid based upon the song they sing. Presented in the right way Suelen's "magic" might be acceptable to the Ugaro, after all, this tribe just agreed to let Aris live and he actually is a sorcerer. Unfortunately, the Ugaro tend to debate things over several days and both Lao and Ugaro are dying of their injuries. 

Suelen fits in very well as a continuation of Tuyo, although the characters do not appear in the other books except for brief appearances by Aris and Ryo. The main downside to this series is the haphazard order of publication. Chronologically, I would now suggest reading Tuyo, Suelen, and then Tirshana, books 1, 5, then 3. Also annoying is the availability of various formats. Tuyo is available through Barnes and Noble, Amazon, and Audible. Tirshana and Suelen are available in ebook, paperback, and hardback through Amazon. Tirshana is also available on Audible.