Injured Ethelred the Unready is one of only three elite carrier pigeons trained to undertake two-way flights. Konstantin von Essen is the traumatized 14-year-old son of Generalfeldmarschall Dieter von Essen, the Commander for Operations in the North Zone of Occupied France. Eleven-year-old Dottie Latymer is evacuated from London to Surrey where her Anglo-American identity, together with her affected American accent, makes her a target for bullies. Rose Clarke, Dottie's only friend, has a violent father and a mother struggling with mental ill-health. Together, they must overcome their personal obstacles to supply MI5 with game-changing intelligence.