The Monstore byTara Lazar

"The Monstore is the place to go for all monsterly needs. Which is perfect, since Zack definitely has a monsterly need. The problem? His pesky little sister, Gracie, never pays attention to the "Keep Out" sign on Zack's door, the one he made especially for her. 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!"--Résumé de l'éditeur.