Adrien Dufourquet, Jean-Paul Belmondo, an airman on an eight-day leave in Paris to see his fiancée Agnès Villermosa, Françoise Dorléac, is pulled into a dangerous chase when two South American Indians steal an Amazonian statuette from the Musée de l'Homme and force Prof. Norbert Catalan, Jean Servais, into their car. Catalan had once accompanied Agnès' father on an expedition into the Amazon, where her father died, and he believes the statuette is one of three keys to a hidden treasure.
Adrien arrives at Agnès' flat just in time to see the kidnapping, the only person who knows the location of her father's statuette. He borrows a ticket and boards the same plane, telling the pilot that his fiancée has been kidnapped, but Agnès has been drugged and does not recognize him. The pilot plans to arrest him on arrival in Rio de Janeiro, but Adrien slips away and escapes.
With the help of Sir Winston, a Brazilian bootblack [Ubiracy De Oliveira], Adrien rescues Agnès. They retrieve the buried statuette, but the Indians steal it from them again.
In a stolen car provided by Sir Winston, Agnès and Adrien head to Brasília to meet Señor Mario De Castro, a wealthy industrialist who possesses the third statuette. On the way they come across the Indians' car with Catalan slumped inside; after they rescue the professor, they press on to Brasília, where Adrien manages a daring escape from pursuing gangsters by crossing between two skyscrapers under construction on a cable. The feat feels like a stunt straight out of a thriller, accentuating the film's breathless mood.
At a party in De Castro's honor, Adrien and Agnès sense the conspiracy tightening. De Castro escorts Catalan to a secure strong room to reassure him that the statuette is safe, but Catalan murders De Castro and steals the statuette for himself. By the time Adrien discovers the crime, Catalan and the Indians have abducted Agnès again and fled in a seaplane.
Adrien steals a plane and gives chase. He learns from Lola, Simone Renant, the woman who financed Catalan, that Catalan murdered Agnès' father and that Agnès is being held aboard a boat. He races to the vessel, clinging to its side as it moves upstream, and finally docks.
In a floating jungle cafe run by Lola, Adrien learns the full truth and realizes Agnès is being kept on a boat. He boards the boat and fights his way forward, then heads to a grotto where the three statuettes once lined up to catch the sun’s rays and reveal the treasure's location. Catalan heads there too, but Adrien knocks out his remaining accomplices and frees Agnès. Catalan locates the treasure, yet explosions set off by a nearby Trans-Amazonian Highway construction crew bury him with it. Adrien and Agnès flee and return to Paris, just in time for Adrien to catch his train back to his garrison.
As the train pulls away, a fellow soldier shares the week’s wild events with him, and the closing moment hints at more adventures to come: > you'd never imagine what
