Several narratives are woven together throughout the film, including those of de Hory, Irving, Welles, Howard Hughes and Kodar.
About de Hory, we learn that he was a struggling artist who turned to forgery out of desperation, only to see the greater share of the profits from his deceptions go to doubly unscrupulous art dealers. As partial compensation for that injustice, he is maintained in a villa in Ibiza by one of his dealers. What is only hinted at in Welles's documentary is that de Hory had recently served a two-month sentence in a Spanish prison for homosexuality and consorting with criminals. (De Hory would commit suicide a few years after the release of Welles' film, on hearing that Spain had agreed to turn him over to the French authorities.)
Irving's original part in F for Fake was as de Hory's biographer, but his part grew unexpectedly at some point during production. There has not always been agreement among commentators over just how that production unfolded, but the now-accepted story is that the director François Reichenbach shot a documentary about de Hory and Irving before giving his footage to Welles, who then shot additional footage with Reichenbach as his cinematographer.
In the time between the shooting of Reichenbach's documentary and the finishing of Welles', it became known that Irving had perpetrated a hoax of his own, namely a fabricated "authorized biography" of Howard Hughes (the hoax was later fictionalized in The Hoax). This discovery prompted the shooting of still more footage, which then got woven into F for Fake. Interweaving the narratives even more, there are several pieces of footage in the film showing Welles at a party with De Hory, and, at one point, De Hory even signs a painting with a forgery of Welles' signature. Some of Hughes' career is outlined in the form of a parody of the "News on the March" sequence in Citizen Kane. Welles also draws parallels between the De Hory and Irving hoaxes and his own brush with early notoriety by including a recreation of part of his 1938 War of the Worlds radio drama, which had simulated a newscast about a Martian invasion and sparked panic among some listeners.
Exactly one hour before narrating Kodar's story, Welles promises that everything in the next hour of his film will be true. Exactly one hour later, the film tells a story where Kodar sits for a series of nudes for Pablo Picasso after getting him to agree to give her the finished portraits, and then selling not those very portraits but fake Picassos in their place. The story climaxes with Welles and Kodar re-enacting a tense exchange between Picasso and Kodar's grandfather, the alleged forger of the paintings, before Welles reminds the viewer that he only promised to tell the truth for an hour and that "for the last 17 minutes, I've been lying my head off."
In the commentary to the Criterion Collection DVD release of F for Fake, Kodar claims the idea for this segment as her own. She also claims credit for the movie's opening sequence, which consists of shots of a miniskirt-clad Kodar walking down streets while rubbernecking male admirers (unaware that they are being filmed) stop and openly stare. This sequence is described by Kodar as inspired by her feminism.