The almost offhand efficiency of her reconstructive surgery and the speed of her recovery may seem jarringly implausible; likewise the film's impelling idea that the old boyfriend she seeks out would not suspect who she was.
But if we take a breath and a step back and treat the film as a sustained allegory about Germany's inability to come to terms with herself, it assumes a breadth and depth that mark it out as a masterwork.
The old boyfriend is Johnny (Zehrfeld, who was Hoss' co-star in Barbara), a pianist in the bar of the title - its lurid, neon glow spilling out into the rubble-strewn streets makes it seem like the gates of the underworld.
For good reason, Nelly conceals her true identity from Johnny, introducing herself as Esther; he, struck by her similarity to the wife he believes dead, hits on a scheme to have "Esther" impersonate Nelly so as to liberate the fortune to which she, the only survivor of a wealthy family, is entitled.
To do so, he must remake her, in her own image.
It's a story saturated with irony and rich in metaphorical potential and Petzold, who co-wrote the screenplay from elements of a 1961 French novel The Return from the Ashes, mixes it all into a potent brew before delivering a killer climax.
Hoss, surely the foremost German actress of her generation, gives a powerhouse performance, full of pain and longing, and the use of the Kurt Weill and Ogden Nash classic Speak Low is a masterstroke. Highly recommended.
Verdict: Finely wrought thriller.
Cast: Nina Hoss, Ronald Zehrfeld, Nina Kunzendorf
Director: Christian Petzold Running time: 98 mins
Rating: M (adult themes) In German with English subtitles