The Dragon's Eye by Dugald Steer
When Daniel and his sister Beatrice spend their summer with Dr. Ernest Drake, they find themselves propelled into the world of dragonology - the science and protection of dragon-kind. Soon the siblings are caught up in a race to find the Dragon's Eye, a jewel that has the power to reveal the identity of the true Dragon Master. But evil dragonologist Ignatius Crook will stop at nothing to claim it for himself. The first in four fire-breathing novels that are packed with dragons, magic and action-adventure.