When Scabious Dankhart engineers an outbreak of deadly spores called Ice Diamonds, causing chaos and illness, twelve-year-old Angus, who can predict and control catastrophic weather, and his school chums must find the legendary Lightning Heart--a stone of great power--in order to put everything right.

In order to throw Dankhart off their trail, Angus, Dougal, and Indigo go into hiding, but when they discover the existence of blue dragon scales that would allow a storm prophet to control multiple fire dragons, Angus and his friends go on a quest to locate all four scales.