When a German plane that 11 year old Tom Mullen is unable to identify crash lands in a nearby field to his home in the small Kent village of High Halden, he is eager to find out more. Arriving at the site, he sees the solitary pilot being taken away by soldiers of the Home Guard but then sees a young boy climb out from a hatch on the side of the aircraft and run towards a nearby wood. Tom gives chase only to discover the boy is also German and after finding out his name is Kristian Muller, he has to protect him, even if it means having to lie to his two friends, Matthew and Beth.
Meanwhile, a German spy is in the area collecting information on the temporary airfields being set up for D-Day and sending secret messages back to Germany from a safe house. With a team of spy hunters on the trail including Alex, the boyfriend of Tom's older sister, as well as the father of his school nemesis, Tom realises that Kristian could be in danger and has to do what he can to get this boy back home.
Blitz Boy is a heartwarming tale of forbidden friendship in time of war.