The Carnelian (Gemstone Chronicles #1) by William L. Stuart (Self-Published, 2012, 242pp.)
Aidan, his little sister Maggie, and their grandparents, Beebop and Nana, find themselves drawn into the magical realm of Celahir after they accidentally free Findecano, a Light Elf who has been imprisoned for centuries in a rock. Findecano explains that he was hidden away in this prison after he discovered a plot by the Dark Elves to steal the gemstones from the magical Elven Bow. The family accompanies him deep into the heart of Celahir to to recover the first of the gemstones, the Carnelian, which is reported to be in the clutches of a kelpie, a mythical horse-like creature that feasts on human flesh. While the set-up is a bit slow, the pace really picks up after the family departs our world for the magical realm of the elves. A lovely fantasy adventure that will appeal especially to children ages 9-12.
Click on cover for image source.