Small-time con man Konrad Kujau needs to make money; to do so, he decides to forge Hitler's diaries, one of which ends up in the hands of Stern magazine reporter Gerd Heidemann who is determined to get his hands on more.

In search of evidence that the diaries could have been lost in a plane crash carrying Hitler's personal belongings during the fall of Berlin, Heidemann travels to the East, where he meets a pair of East German secret police officers.

Stern demands an expert opinion on the diaries, so Kujau submits letters he also forged for an expert handwriting comparison; Heidemann travels to Boston to buy the publication rights to the diaries from Hitler's cousin.

A media mogul ends negotiations to republish the diaries in the U.S.; Heidemann sets out to convince him, accidentally leaving behind a folder with pages from the diaries.

The Stern special edition must be rushed to print, but the editors don't know about the diaries; when Elisabeth speaks openly about her belief that they are fake, she finds herself out of a job; Kujau puts Heidemann under pressure.

The West German criminal police conduct a scientific examination and issue the final word on the authenticity of the diaries; Kujau, after a brief escape attempt, returns to face punishment and fame.