Strange and terrifying things are happening in New Marburg: people are disappearing and changing into characters from the Grimm fairy tales.

When twins Willow and Jake Grimm move to the isolated town where their parents work for a top-secret Think Tank, they are amazed to discover a place where people jetpack to work, robots direct traffic, and senior citizens battle with lightning-swords.

But after a freak lightning storm, which transforms the twins' school into a medieval castle—complete with a moat, drawbridge, and a giant who looks strangely like the school's overly aggressive hall monitor—the twins discover the truth: just like their ancestors, the original Brothers Grimm, Willow ad Jake are Grimmwalkers. And just like their ancestors, they have been transported to the place where all fairy tales are born. The most dangerous place in existence: Grimmworld.

But before the twins can figure out how to get home, they learn their best friends have been transformed into the fairy tale characters Hansel and Gretel and have been imprisoned by a candy-obsessed wicked witch.

Now, aided only by their wits, their courage, and their love for each other, the twins must venture deep into the Cursed Forest to save themselves and their friends. And maybe—just maybe—save the universe from falling into the clutches of the witch in the woods.