Mr. Billion is a comedy and road movie that features John Cutler (Jackie Gleason), executor of the vast estate of newly deceased billionaire, Anthony Falcone. Cutler always assumed he would inherit and control Falcone's corporation and is shocked to discover that an unknown nephew in Italy, working as a mechanic, has been named the sole heir. Guido Falcone (Terrence Hill) must travel to San Francisco within 20 days to inherit the estate, which will be difficult given Guido's fear of flying. If time runs out, Cutler will inherit instead, and he is doing everything possible to make this happen. He sends Rosie Jones (Valerie Perrine) to persuade Guido to sign over his claim to the estate, but this backfires when she becomes attracted to Guido. Cutler unsuccessfully hires kidnappers to hold Guido for ransom, and places other obstacles in Guido's path as he races against time to get to San Francisco.