What is it like to be a ghost? Especially one who does not even realize at first, that she is a ghost. And when she does, she cannot understand why she is "ghosting." She is bewildered, troubled and is looking for someone to help her solve the mystery. Rosie feels there is something she has to do, but what? What is it like to befriend a ghost? Bethan and Joshua, visiting London with their grandparents, are about to find out... Their adventure takes them from present-day, cosmopolitan city, back through time, to the London of World War Two, during the blitz, where they share the experience of air-raids, bombing, fear and - on the night of a bomber's moon - devastating and loss. This starts them on a trail to seek out anyone still living who may have information that could ease their friend's disquiet. But their time in London is coming to an end... And Rosie's time, too, is running out. Can they help her find peace?