At the back of Frankensweet’s Candy Shoppe, under the last box of sour gumballs, there’s a trapdoor. Knock five times fast, hand over a bag of squirmy worms, and you can crawl inside The Monstore. The Monstore is the place to go for all of your monsterly needs. Which is perfect, since Zack definitely has a monsterly need. The problem? His pesky little sister, Gracie, who never pays attention to that “Keep Out” sign on Zack’s door—the one he has made especially for her. But when Zack’s monsters don’t exactly work as planned, he soon finds out that the Monstore has a few rules: No Refunds. No exchanges. No exceptions.