Willy Fog, a wealthy middle-aged gentleman, occupies 7 Savile Row in London. His fortune's origins remain undefined. He adheres to strict punctuality and routine, timing daily activities meticulously and dismissing a previous servant over incorrect shaving water temperature. Solitary and without family, his sole social interactions occur at London's elite Reform Club, where he plays billiards and reads newspapers. His ordered existence fractures during a club debate about an 80-day global circumnavigation theory. When elderly Lord Guinness proposes attempting the journey if younger, and others mock him, Fog defends Guinness's honor. He wagers £20,000 with four members—Sullivan, Farrel, Johnson, and Weston—that he can circle the world in eighty days, departing London that evening (October 21st, 1872) and returning to the club by 8:45 PM on December 21st. Hours before leaving, he hires Rigodon, an ex-circus performer desiring calm employment. Unaware to Fog, Inspector Dix and Constable Bully of Scotland Yard pursue him, suspecting him of the Bank of England robbery, while saboteur Transfer, hired by Sullivan, schemes to thwart the wager.

During the journey, Fog exhibits unshakeable composure, rationality, and resourcefulness against obstacles including Transfer's sabotage, transport failures, natural disasters, and false arrests. He uses wealth to overcome barriers—purchasing transport or incentivizing aid—but also demonstrates physical courage, skillfully employing non-lethal "Cane Fu" with his cane while refusing firearms even in hazardous locales like San Francisco. Initially focused solely on the wager, he reveals unexpected compassion in India upon learning Princess Romy faces sati (funeral pyre sacrifice). Risking time and resources, he rescues her, stating he acts charitably "when I have the time," marking a pivotal display of empathy.

Romy joins Fog's group seeking relatives in Singapore. Discovering their death, Fog invites her to England. A subtle romance develops as Fog grows protective of Romy and forms loyal camaraderie with Rigodon and Rigodon's companion, Tico. Evolving from solitary habit to dependable leader, he confronts mutiny aboard the Henrietta and natural disasters with unwavering calm. His "Stiff Upper Lip" persists; he faces crises with optimistic resolve, avoiding panic even during wrongful arrest in London or near journey's end.

Though Fix's arrest seemingly makes him miss the deadline by minutes, an International Date Line error is uncovered. Fog rushes to the Reform Club, winning the wager with seconds left. Transformed by the journey, he values the experience and relationships above regained wealth. He marries Romy, finds happiness, and deepens mutual respect with Rigodon and Tico. His arc concludes by exchanging isolation for companionship and adventure, embarking on subsequent voyages adapting Jules Verne's "Journey to the Center of the Earth" and "Twenty Thousand Leagues Under the Seas."