American architect Stourley Kracklite has been commissioned to construct an exhibition in Rome dedicated to the architecture of the 18th-century French architect, Étienne-Louis Boullée, who until the 20th century remained little known. Kracklite's Italian colleagues express doubts about whether Boullée really belongs in the architectural pantheon; they note that few of his buildings were ever constructed and observe that Boullée was an inspiration for Adolf Hitler's architect Albert Speer.
As he works on the exhibition, Kracklite's marriage and health deteriorate. He becomes obsessed with Caesar Augustus, the first emperor of the Roman Empire, after hearing that Augustus's wife, Livia, supposedly poisoned him. Suffering from recurrent stomach pains, he suspects his much younger wife, Louisa, of trying to do the same. Louisa reveals that she is pregnant with Kracklite's child, conceived at the precise moment their train crossed the Italian border. Meanwhile, she has become sexually involved with Caspasian Speckler, the younger co-organiser of the exhibition. We learn that Caspasian has also been siphoning off funds from the exhibition, even as he and his Italian associates undermine Kracklite's authority and confidence. Kracklite himself is seduced by Caspasian's sister Flavia, a photographer in her apartment across from the Palazzo della Civiltà Italiana. The two are discovered in flagrante by Caspasian, who threatens to tell Louisa.
Louisa leaves Kracklite, who is diagnosed with stomach cancer and given only months to live. The film ends at the exhibition's opening ceremony, nine months after their arrival in Italy. Kracklite, now replaced as director by Caspasian, watches from a high vantage point as Louisa cuts the tape. As she suddenly goes into labor, Kracklite jumps to his death.
