It is 1940, the time of the Phoney War. Britain stands alone with German invaders waiting across the Channel and an anxious population preparing for the bloody battle ahead. In an isolated girls' boarding school, sixteen-year-old Judy Randall watches the coming of war with a mixture of fascination and fear. She is a misfit in an institution that prizes conformity; a Catholic with Jewish heritage at a time when anti-Semitism is still commonplace. Most inconveniently of all, she is autistic, and her behavior is misunderstood as merely eccentric and insolent.

Bored and frustrated by her inability to help the war effort, Judy becomes obsessed with the idea that her hated headmistress is a Nazi, and she goes to increasingly reckless lengths to prove her theory. In the meantime, the adults of the school busy themselves with planning how best to protect the children in their care if occupying forces overrun the country. For teacher John Peterson, who has seen armed conflict before, his own agonizing history forces him to consider what sacrifices he might have to make if the horrors of the war overtake them all.

A Most Dangerous Innocence offers a glimpse into the early days of the Second World War, seen from a sleepy corner of Britain. It is also a meditation on childhood guilt, innocence, loyalty, and the courage to stand alone.