Diadem - Book of Time

"Shanara decides to reveal her history to Score, Helaine, Pixel and Jenna in her own unique way -- by creating a realistic illusion from her memories. But a powerful sorcerer hijacks her spell and transports the five of them back into the past instead. Now instead of seeing Shanara's troubled story, they are forced to live it. But if they change anything -- anything at all -- they might wipe out the future ... including themselves"--Page 3 of cover.