Izzie is living in London with her mum and two younger brothers - she hasn't been to Swallowcliffe since she was small, but after a bout of tuberculosis, she is sent down to stay with her Gran, Polly, who is still a housekeeper at the Hall. While there she meets a German refugee, Andreas, who has been taken in by the local shopkeeper.

It doesn't look like he's being treated too well, so Izzie helps to get him work at the Hall. But as the threat of a war with Germany increases, people are suspicious of Andreas, and when a fire breaks out in Lord Vye's attic studio, nearly killing one of his daughters and Izzie's Gran, the finger is pointed at the German interloper. Can Izzie prove his innocence?