The titular Echorium, on the Isle of Echoes, is home to the Singers: people trained in the use of the five Songs of Power. The trilogy follows the adventures of three successive generations of young Singers and their friends.
This series provides examples of:
- Amplifier Artifact: Bluestone and khiz-crystal both amplify the Songs, as well as allowing them to be transmitted over distances.
- Anti-Magic: Among other things, khiz can be used to resist the Songs.
- Empty Shell: At its most extreme, the death song Yehn induces a form of living death by "closing doors" in the head.
- Ghost Memory: All quetzal have access to the "Memoryplace", the stored experiences of their kind. Yellow Flowers allow humans to access it too.
- Magic Music: Appears here in the form of the five Songs of Power taught in the Echorium, each used for a specific effect. Certain stones can increase their effect, as can singers working in a group, and for some reason the color blue.
- Mind-Control Device: Khiz is used throughout the series to control people and manipulate memories.
- No One Could Survive That!: The phrase is used almost verbatim in relation to Frazhin. Turns out he did.
- Our Centaurs Are Different: Intelligent, more or less neutral, and avoidant of humans.
- Our Mermaids Are Different: The merlee lean more towards the "obvious sea creature" than "pretty people with legs" end of the scale.
- Raised by Wolves: Shaiala is a human girl raised by a herd of centaurs. She uses their fighting techniques (despite only having half the legs they're designed for), and her inability to break rocks to get a herdstone presents an issue for her.
- Rite of Passage: To join a herd, young centaurs must travel to a certain canyon and obtain a herdstone. They break them out of the rock by kicking it: a bit of a problem for Shaiala, since she doesn't have hooves.
- Snake People: The naga.
- Winged Humanoid: Quetzal are half-bird, half-human. Not only do they have the Winged Humanoid arms-and-wings setup, they have beaks, and are covered in feathers.