Set on the Isle of Man during the First World War, the novel relates the life of Mona Craine, a young woman who lives with her brother and their aging father. Mona's life is disrupted first by her brother being called up to fight in France, and then by the authorities agreeing to set up an internment camp for enemy aliens there at Knockaloe. Mona consents to live there still and supply food for them odious Germans against her wish and only for the sake of her ill father. However, her hard and unforgiving attitude towards the Germans begins to lessen when she meets the polite and well-spoken Oskar Heine. As they begin to fall in love, they also need to deal with the fierce hostility of the local community.