The spy at the window

It's 1939 and war has broken out. Everything has changed at Highbury House school. There are no servants, for one thing, and the pupils have to help with domestic tasks. Then a boys' school is evacuated to the Romney Marsh, billetted in the same building although, of course, contact with the boys is strictly forbidden. Despite this, Justice soon strikes up a friendship with Henry, a boy who shares her dislike of games lessons. Then Justice's father suddenly goes missing. Could he be a real-life spy? Can Justice and her friends find her father - before any secrets leak?