The Singers have many special abilities, the most important of which is knowledge of the Songs of Power: Challa for sleep, Kashe for laughter, Shi for sadness, Aushan for fear and Yehn for death.

Although Frazhin was apparently killed by quetzal after the Battle of the Merlee at the end of Song Quest, and finished off by being sung Yehn over a distance, his body was never recovered.

Renn, a gifted but often bullied Eight Year novice in the Echorium who can speak to Half-Creatures, is asked to assist the Singers by translating for Shaiala Two-Hoof, a wild girl brought to the Island for treatment, who claims to have been raised by centaurs.

Although initially the pair argue, meeting Rialle helps to calm Shaiala and she begins to remember, enough to reveal that her memories were wiped using a mask made of khiz.

Second Singer Kherron takes this excuse to insist that Shaiala and Renn leave with him to search for Frazhin, the escaped khizpriest whose body was never found.

Upon arrival, the group begins to explore Southport and Shaiala, despite being closely guarded by a pentad of orderlies including Frenn and Lazim, escapes, only to become lost in the rough part of the city.

After a brief confrontation, the two groups agree to work together, and the Horselords tell the Singers about the Sunless Valley, reachable only through the Pass of Silence, where they suspect the children have been taken.

However, there is trouble in the Valley - Shaiala and Erihan have arrived to find the captured centaurs working as slaves to mine khiz, and have freed them with herdstones, leading a revolution.

With the Khizalace shattering around them from the blow, the Harai flee, and Shaiala and Renn hurry to free Kherron, whose voice is badly damaged from the crystal, then join the battle outside.

With the arrival of the Kaleri, the battle has turned in the Singer's favour, at least until Yashra appears and seals the gates against them with khiz power, trapping them inside.

Although she seems victorious, capturing Erihan as a hostage and controlling the khiz against the Kaleri, she is distracted when Singer Kherron warns her to keep an eye on Frazhin, who is trying to escape without her.

Shaiala joins the Kaleri to learn to be a tribeswoman from Erihan's mother, and Renn returns to the Echorium, where he reconciles with Rialle and the merlee.

The plot is similar to Song Quest as the story follows young novices who have the chance to adventure outside The Echorium, which is rare for their age.

Crystal Mask relies on Song Quest its storyline to be understood; for example about Renn's parents and concerning the centaur tribes.

[1] The Echorium Sequence uses themes from Ursula K. Le Guin's Earthsea and Anne McCaffrey's Pern in the sense of merlee and half creatures in conjunction with human beings and singers.

The usage of half-creatures is a theme throughout The Echorium Sequence as the general plot behind each of the three novels concerns or involves half creatures or mentions of them through references.

Some of the main characters in Song Quest feature in Crystal Mask, following on 20 years into the future but do not have a major part within the storyline.

At the beginning is a scene set in a history lesson being taught by Singer Ollaron who refers to events 20 years in the past that occurred in the novel Song Quest.

[1] Also, Goodtoread.org said, "The characters of Renn and Shaiala who interest the reader at first quickly become pale and flat plot devices with only occasional moments of relief and colour.

"[1] Kirkus Reviews said, "It is difficult to distinguish heroes and villains on the basis of either their actions or their attitudes," referring to the fact that the main characters appear aggressive and violent towards each other as well as ignorant and abusive.

Kirkus Reviews also said, "As the final confrontation sputters into an inconclusive anticlimax, the one interesting revelation, which might explain some contradictions, is pointlessly repudiated," referring to discovery of Renn's true parents.

"[4] The majority of reviewers raised the point that the novel was poorly concluded and lacked a climax and interest at events such as the discovery of Renn's true parents and the destruction of Yashra's palace.

The School Library Journal said the world she has created is original and detailed [5] with cliff hangers and realistic responses from the characters to situations raised in the plot.