The film tells the epic journey of a 9-year-old boy named George (played by Elliot Heffernan) in London during World War II. His mother Rita (played by Saoirse Ronan) sends him to the safety of the British countryside. George is indomitable and determined to return to Rita and his grandfather Gerald (Paul Weller) in east London, so he embarks on an adventure, only to find himself in great danger, while the distraught Rita is looking for Her missing son.