Stones of Fire (Time Treaders #2) - Hamm, Jeris G

Young teen Matt Silvers must capture the Stones of Fire and rescue the Guardian, Jasper, from the clutches of the evil Wolvin. As a Valenian protégé, Matt travels to Scotland and battles Druid thieves while his best friend, Ryan, must escape the paralyzing grip of the Rim. Meanwhile, in his hometown of Baywood, his friend, Julie, faces lizard invaders from the Dark Void.

The second novel in the Time Treaders series