The last time Momo saw her father they had a fight—and now all she has left to remember him by is an incomplete letter, a blank piece of paper penned with the words "Dear Momo," but nothing more. Moving with her mother to the remote Japanese island of Shio, Momo soon discovers three yokai living in her attic, a trio of mischievous spirit creatures that only she can see and who create mayhem in the tiny seaside community as she tries desperately to keep them hidden. But these funny monsters have a serious side and may hold the key to helping Momo discover what her father had been trying to tell her.