Who is the visitor from the other side?

Nora is 15 years old. Her parents died when she was young and now she lives with Anders and Karin and their son Dag. They move into an old apartment in an old house in Enköping. Behind a wall they find some old items from people who lived there a long time ago. They also discover that their apartment is haunted by a ghost. Together with Dag, Nora tries to find out more about the people who lived there.