When the Sandman asks Mona, a feisty yet kind-hearted eleven-year-old, to be his apprentice, she jumps at the chance to escape her unsettled life at the orphanage. But trouble has a way of finding Mona, and it doesn't take long for hijinks to ensue when she accidentally unleashes the evil Boogie Man from his magical prison. Before Mona can come clean, Boogie kidnaps the Sandman and takes him to The Land of Nightmares-a dark place where clowns are anything but funny and bed bugs really bite. Needing to make things right and prove she doesn't mess up, Mona teams with a hyperactive sloth and a dubious guide she doesn't trust to rescue the Sandman. But saving the day won't be easy, and Boogie has a powerful magic that could stop the world from dreaming forever.