Maud is an orphan, and not the best behaved, so she and everyone else are surprised when she is adopted by two spinster sisters and brought home to live with them (and a third sister). She's in heaven with new clothes and books and vows to be on her best behavior always, but things are a little strange at home. She's a secret child, always kept inside or in the walled in garden so that the neighbors don't know she exists.
Eventually Maud is brought into the "family business" of doing seances for wealthy people who want to contact their dead loved ones. Maud's job is to hide and, at the right moments, join in with the singing or cause objects to move. Maud does her very best, because she wants more than anything to make her favorite guardian, Hyacinth, love and praise her. But she starts to wonder if the things they are doing are right.