Stas Tarkowski and Nel Rawlison live with their fathers and grow up in the city of Port Said. Their fathers are engineers who supervise the maintenance of the Suez Canal. One day an anti-British rebellion begins in Sudan, led by a Muslim preacher Mahdi. Stas and Nel are captured as hostages by a group of Arabs who hope that they can exchange the children for Fatima, Mahdi's distant relative, who had been arrested by the British at the beginning of the novel.