Huey, Dewey and Louie manage to decipher the code written on the map, but they refuse to tell it to Scrooge unless he allows them to join him on his treasure hunt. Just then, Scrooge's main rival Flintheart Glomgold pays a visit, wanting to buy Scrooge's candy factory for $2,000,000. He makes a bet with Scrooge in which one of them must try to earn more cash than the other within two weeks. (The loser has to eat Glomgold's hat.) Scrooge agrees to this bet, and allows the boys to join him, since they know where the sunken treasure ship they're going after is - Ronguay, South America! Unbeknownst to the good guys, Glomgold is getting some help of his own from El Capitan. The ducks take a cheap plane that they soon realize is going in the wrong direction. Upon realizing this, they storm the cockpit and find out that the pilot is a cheaply-made robot from Glomgold's company; this raises Scrooge's suspicions.
After landing in Ronguay, they are stampeded by fleeing citizens who take off in the plane. Scrooge gets some supplies and a llama from a nearby supply store, whose owner tells him that the Monsapis are coming. He and the nephews trek off into the desert, during which Scrooge almost sinks into some quicksand that he didn't see because the "Danger" sign was sawed off. As Scrooge suspects, Glomgold is trying to sabotage the journey so that he and El Capitan can find the treasure ship first. They have an imprint of the map from Scrooge's chocolate, which they are keeping solid by way of an ice cream cart pulled by a pack mule. Glomgold throws some dynamite in Scrooge's direction, but when he and El Capitan turn around to discover that their pack mule has eaten their chocolate map, he is forced to snuff the fuse. At this point, the Monsapis, a centennial series of torrential rain and flooding, begin to occur, scaring off Scrooge's llama. Scrooge and the nephews manage to find a cave that looks just like an upside-down ship, but they find nothing upon entering. They stop here to rest, but before doing so, the nephews set up a Junior Woodchuck alarm.
When Glomgold and El Capitan show up, they set off the alarm, awakening Scrooge and the boys. Glomgold and El Capitan then manage to climb out of the flooding cave and try to trap the Scrooge and the nephews within. Fortunately, Scrooge and the nephews do not go much farther before they find what they've been looking for - a shipwreck full of gold. After repairing the ship and getting it out of the now-flooded Ronguay, it looks like smooth sailing until a gun-toting Glomgold and El Capitan spring out of hiding. Glomgold gloats as he lowers Scrooge and the nephews into the sea on a life-boat. But Glomgold then makes the mistake of tossing one of the ship's many gold coins to Scrooge. El Capitan does not want to lose any of his gold and demands that Glomgold go out and bring it back. Their bickering results in the sinking of the ship, and Glomgold ends up being rescued by the nephews. Since Scrooge has won the bet by virtue of the aforementioned coin, Glomgold must eat his hat. The boys wonder what became of El Capitan, who again swears revenge.