Gottlieb von Cramm, a German tennis star of the 1930s, petitions Holmes for help.
The sportsman is being blackmailed on a matter of the utmost delicacy, and when the blackmailer reveals all to the National Socialist authorities, it is Holmes who comes to the rescue by asking Reichsmarschall Herman Göring to intervene.
But is the better than expected outcome to the case a result of Holmes's intervention, or is Cramm's glamourous mother keeping her own role to herself? And why does Frau von Cramm seem so familiar to Holmes?
It is only once Britain is on the brink of another war against Germany that the full truth dawns on Holmes.