No original negatives survive but a high quality nitrate copy is held at the National Film Archive in Prague.

[2] Germany, 1927: Beautiful Russian spy Sonja Baranikowa seduces Colonel Jellusič into betraying his country (an unnamed eastern European one) for her employer, Haghi, a seemingly respectable bank director who is actually the diabolical mastermind of a powerful crime organization.

Haghi seeks to steal a secret Japanese–British peace treaty, which will prevent "war in the East" unless it is exposed, before it reaches Tokyo.

Sonja, who had been tricked into being the one to smuggle the treaty out of the country by Haghi's promise not to harm 326, learns of the crash, races to the site and is reunited with her love.

According to Robert Osborne, Lang was having an affair with Maurus during filming, even as his wife Thea von Harbou was involved writing the screenplay.

In spite of this, Klein-Rogge worked with Lang and Harbou on various notable films, including Destiny (1921), Dr. Mabuse the Gambler (1922), Die Nibelungen (1924) and Metropolis (1927).

[4] Regarding the casting of Agent 326, Lang surprisingly went for the upcoming teenage idol Willy Fritsch, whom he had seen in one of his by then typical juvenile lover parts in the silent film The Last Waltz (1927).

[5] Spione was made at a substantially reduced budget as the studio looked to cancel Lang's contract following the poor commercial return of his previous film, Metropolis.

[7] Philip French of The Guardian wrote that the film "weaves together recurrent Lang themes of fate, fear, power and paranoia into a dynamic conspiracy thriller".

"[9] Matthew Thrift of the British Film Institute meanwhile singled out the opening sequence as "a marvel of narrative economy in montage".

[6] A 143 minute version was restored in 2003–2004 by the Friedrich Wilhelm Murnau Foundation thanks extensive research and co-operation with repositories all over the world.