Book of Thunder
Score, Helaine, and Pixel rush to the planet Dondar to rescue their unicorn friends. Thunder, the noble leader of a herd has lost his title – and almost his life – to Tychus, a rogue unicorn who has a "wrongness" about him that everyone senses. And Helaine notices that the herd is behaving oddly, as if under a spell, with Tychus in charge.
With help from their magical guide Oracle, the wizard Shanara and her sleepy red panda named Blink, and a unicorn named Darkstar, the trio learn more about the new leader of the unicorn herd and his devious scheme that will endanger the entire Diadem.
John Peel
John Peel (born 1954) is a British writer, best known for his books connected to several television series. He has written under several pseudonyms, including John Vincent and Nicholas Adams. He lives in Long Island, New York and his wife is a U.S. citizen, but Peel still travels under a British passport.
Diadem
Also known as Diadem: Worlds of Magic.
Diadem consists of ten books. The current recommended reading order for the series is provided below.