How hard can it be to write a fantasy trilogy? When YA author Philip Murdstone's star starts to wane, his agent, the ruthless Minerva Cinch, convinces him that his only hope is to write a sword-and-sorcery blockbuster. Unfortunately, Philip is utterly unsuited to the task. In a dark hour, a dwarfish stranger comes to his rescue. But the deal he makes with Pocket Wellfair turns out to have Faustian consequences.

Three middle school girls—Misha, June, and Ollie—know their epic fantasy story could be the next Lord of the Rings or Game of Thrones. The only holdup is they have to write it first. But that’s a trifling concern: they’ve bought a $1.99 composition notebook, and they’re going to pass it back and forth over the course of their 7th grade school year to build the world and characters as a team. Together they invent and explore the mysterious...