In the Chief's office, he explains to Marie that Austrian military forces have been suffering terrible losses due to a security leak, and he has been on the lookout for an attractive female to serve as a secret agent to help expose the man he thinks is the traitor: Colonel von Hindau, who is attached to the chief of staff of the Austrian army.

She accepts the offer, remarking that, rather than the generous compensation the Chief promises, what primarily appeals to her is the opportunity to serve "the cause of Austria."

During her faux seduction, the Chief places a telephone call to Hindau, requiring that he briefly absent himself and leaving X-27 free to search his personal belongings.

Hindau returns from his phone call and, discovering his cover is blown, offers his compliments to X-27, retrieves his service revolver, and kills himself.

The secret message leads X-27 to a casino, where she finds the man who had given Hindau the cigarette, who turns out to be Colonel Kranau, a Russian spy.

They flirt a bit more before X-27 calls Kranau a clown, to which he responds that he is a soldier who sometimes crosses enemy lines and engages in subterfuge, whereas she uses her sexuality to "trick men into death".

Behind enemy lines and accompanied by her black cat, X-27 disguises herself as a dimwitted peasant girl and gains employment as a chambermaid in the Russian officers' quarters.

When he performs the atonal piece on the piano, he realizes it is a code and promptly burns the score, confident he has thwarted X-27's mission.

Marie makes two requests of a monk that visits her while she is awaiting execution: that she be furnished with a piano in her cell, and that she be permitted to wear the clothing in which she "served, not my country, but my countrymen" (that is, what she wore as a streetwalker).

Sternberg based his "espionage melodrama" loosely on the exploits and demise of Dutch spy Mata Hari, with screenplay by Daniel Nathan Rubin.

He said "the lady spy was not dishonored, but killed by firing squad", and felt the chosen title would distort the significance of the heroine's death.

The movie was rushed into production by Paramount to capitalize on the critical and popular success of Sternberg's films The Blue Angel and Morocco the previous year, both of which starred Marlene Dietrich.

M-G-M studios, alarmed by the competition that the Sternberg-Dietrich phenomena posed to star Greta Garbo, responded with the copycat Mata Hari the same year.

"Court Officer: "As a matter of record, tell me why a woman charged with important work should permit or aid the escape of a dangerous enemy.

"As film historian Andrew Sarris observes: "Yet it is Dietrich who ultimately passes judgment on her judges by choosing to die as a woman without a cause in a picture without a moral.