Rosie has always taken care of herself and her mother in their house overlooking the coast of Maine. Her mother is very detached and doesn't always recognize her daughter, although she is able to keep up with her data entry job and bring in enough money that Rosie can order groceries and supplies for them online. Rosie has coped with the stress of this by writing stories, and also by hanging out with her supportive friend, Germ. Germ, however, is starting to develop older interests, and tells Rosie that her stories are childish. Rosie burns her stories, which leads to her, as well as Germ, developing the ability to see the ghosts that live in her house. One of these spirits seems especially threatening, but some are supportive. Ebb, the ghost of a young boy, has always watched out for Rosie. He takes her to meet Homer, who tells Rosie some information about her and her family that might account for the new threats. Rosie's mother was the last witch hunter, and the Memory Thief, a witch, has stolen her memory to try to stop her from hunting any more witches. Rosie now has these powers, but must find out on her own what she needs to do. The ghosts help, as does a book her mother had hidden. Rosie must create a magical item she can use as a weapon, delve into the mysterious past of her family, and find a way to save her mother as well as many of the ghosts who surround her. Even after all that, Rosie has angered another witch, the Time Witch, and will have to face off against her, with Germ by her side.