The Blitz Business opens in London's East End on December 29, 1940, when the Blitz is at its worst. Jamie is almost 15, has mild retardation, and lives with his grandmother and cousin Roy as a virtual shut-in. He wanders away from home and soon finds himself in the midst of circumstances beyond his comprehension. He survives many harrowing predicaments, including one that tests his courage when someone he loves is in mortal danger. He feels hope and despair in turn as he struggles to make his way after a confusing evacuation to the Hampshire countryside.

In spite of a life of deprivation, Jamie learns and grows over the next year, endearing himself to just about everyone he meets, some of whom will fight for his right to lead a normal life. But the authorities have their own ideas about his proper place, and his past is still not entirely behind him. When a German spy's mission intrudes, things get out of hand. His life careens between catastrophe and hope as Jamie fights to make the best of situations he cannot control.