Right from the start of the novel it was clear that this was not a book about espionage and intrigue, as the title suggests. As the first and last lines of the prologue suggest, the Spion, or spyhole, is used as a means of looking at the neighbours, and it becomes clear that sight is an important theme in the novel.

Beyer also uses sight through the use of the photo album which provides the protagonist, Carl, and his cousins, with more questions than answers as they look through it. Who was the opera singer with the same Italieneraugen as the children, and who was the grandmother who mysteriously died young? The main family secret, however, involves the grandfather, who left his fiancée in 1936 and disappeared without a trace. It is implied throughout the book that he was part of the Condor Legion, volunteers from the German Luftwaffe who gave aid to the Spanish Falange during the Spanish Civil War. Then, in 1937, they were responsible for bombing Guernica.

By using children as the narrators, the reader is given an alternative perspective on the Third Reich, a technique which proved successful in his earlier novel, Flughunde. In Spione Beyer goes one step further and uses a different age group, as well as a generation that were not even around when these events unfolded.

At times Spione can be confusing because it is narrated as though it comes directly from the characters' heads, which means that we don't always get specifics because the characters already know them. Beyer also alludes to certain events without actually naming them. He sets parts of the novel in 1977, which was the peak of the Deutscher Herbst, a particularly violent period in German history. However, perhaps only the German reader, or someone who is particularly knowledgeable about German history, would recognise this. This makes it a somewhat difficult read at times but overall it is a novel worth reading for those who enjoy trying to work out puzzles and like a little bit of history without having it forced onto them.