Lord Edward Glenarvan and his wife Helena discover a distress message inside a shark's stomach, written in three languages by the shipwrecked Captain Grant of the Britannia. The British Admiralty refuses to send a rescue ship, prompting Lord Glenarvan to mount a private expedition on his yacht, the Duncan. Accompanied by the captain's children, Mary and Robert, and the absent-minded geographer Jacques Paganel, they set sail for the southern hemisphere.
After crossing the Andes mountains, the party traverses the Argentine Pampas, guided by the native Patagonian Thalcave. They encounter extreme droughts, massive floods, and hordes of red wolves, narrowly escaping death multiple times. Young Robert is even carried off by a condor before being heroically rescued.
Upon reaching Fort Independence in the Sierra Tandil, they realize the Indian tribes have migrated north due to civil war, and the prisoners they heard about belong to a different shipwreck. This false trail leaves the travelers temporarily discouraged.
However, a sudden re-evaluation of the damaged document reveals that the captain is actually located in Australia, not Patagonia. The expedition changes course, prepared to circumnavigate the globe along the thirty-seventh parallel to find the missing captain.
Ultimately, the story highlights the unyielding loyalty of a crew, the devotion of children seeking their father, and the relentless pursuit of justice across uncharted lands and seas.
