Book of Thunder is the fourth book in John Peel’s Diadem series. Once again, the story is about Score, Pixel, and Helanie. They think they’re returning to peaceful Dondar, their favorite world, and to their unicorn friends. However, nothing is ever calm and simple. Upon returning to Dondar, the trio is greeted by a frantic Flame, daughter to the Unicorn herdmaster, Thunder. Thunder has been challenged by a bigger, meaner unicorn for control of the herd and its lands. But there’s something off about this new unicorn.
Our heroes set off on a new adventure that involves a wicked wizard, ice dragons, and mind magic. Along the way, they must figure out the mystery of this new unicorn, survive the journey, and save the unicorn herd.
When I was a kid, this books was my favorite of the original six Diadem stories, probably because it deals the most with the unicorns. Rereading it, I find that it’s still one of my favorites because it has a strong, engaging story that would appeal to younger audiences and adults alike.