It is May 1940. The British army has been routed and is awaiting its evacuation from the beaches of Dunkirk.
Winston Churchill asks Holmes to stand by to provide advice on what steps to take in the face of the anticipated aerial onslaught of the Luftwaffe on British airfields.
As German attacks mount, Holmes offers unpalatable advice which Churchill accepts for want of an alternative. As German attacks switch from the airfields to production facilities, Holmes provides additional detective advice on a most unexpected matter. But it is the use to which Churchill puts the advice, which creates a rift between the two men, which remains unresolved at the end of the story.