An earthquake, a flash flood, an avalanche, a volcano, alligators, jaguars, mutineers, and a man-eating Maoris dog the steps of a shipping company owner, a scientist, and the two children of a lost sea Captain as they circle the Earth along the 37th parallel per instructions in a bottled note the scientist has recovered from a shark's stomach. Only certain facts are discerned from the stained note, especially the words "37 parallel". Teenage Mary Grant (Hayley Mills), her younger brother, Robert (Keith Hamshere), and the scientist, French Professor Jacques Paganel (Maurice Chevalier), trick their way aboard the grand yacht, "Persevero II", during a bon voyage party to see the owner of the shipping company, Lord Edward Glenarvan (Wilfrid Hyde-White), the epitome of British aloofness. With the urging of his own son, John (Michael Anderson, Jr.), Glenarvan's luxurious side-wheeler sets sail for the coastal town of Concepcion, Chile in the search for the missing Captain Grant (Jack Gwillim).