The Most Powerful Magic in the World...got lost

Story elements frequently (and cleverly) overlap in Liesl & Po by Lauren Oliver.  Liesl, locked in the attic by her rotten stepmother, is surprised to be visited by Po, a ghost, and Bundle, Po's ghost-pet.  Po and Bundle are from the Other Side, where ghosts hang out until they go Beyond.  Po has a message from Liesl's recently deceased father - he wants Liesl to bury his ashes under a particular willow tree.  Liesl escapes from the attic and is trying to grant her father's wish, but...there's a bit of a mix-up involving two similar boxes, one containing the ashes and the other containing the Most Powerful Magic in the World, recently prepared for the evil Lady Premier.  A lot will seem familiar in a fairy-tale kind of way - an evil stepmother; an orphan; a big, likable, bumbling servant -  but there's a lot of creativity, too, and a gentleness in the way the story deals with Liesl loss and healing.  Soft, black and white illustrations add a nice touch.