The Echorium Sequence is a fictional young adult fantasy trilogy by Katherine Roberts. The trilogy comprises Song Quest (1999), Crystal Mask (2001), and Dark Quetzal (2003) and follows the tales of The Echorium - the singers located on the Isle of Echoes. In the first book, Song Quest, the major characters are singer Rialle, and Kherron. Song Quest is followed by Crystal Mask, which focuses on singers Renn and Shaiala. Dark Quetzal, the third instalment, stars Kyarra and Caell. The trilogy follows each generation carrying on from the previous generation in each book, starting with Rialle and Kherron. The series features mythical creatures such as nāgas, centaurs, and half-creatures. Source: Wikipedia (en)