Mr. Monahan finances a trip to Peru so that Hap Livingston and the Explorers can search for his brother, Burton Monahan. The Explorers encounter difficulty soon after their arrival in Peru. Captain Carter, who brought their supplies to Peru on his boat, refuses to let the group board to retrieve their supplies. The group soon discovers that Captain Carter is smuggling weapons into Peru in boxes that are marked as belonging to the Scouts!

The Explorers and Captain Carter part ways, but their troubles are far from over. Captain Carter turns the natives against the Explorers, and the Explorers must begin their expedition quickly in order to avoid being attacked. Soon after their departure, Hap becomes very ill, and all of the men who were hired to carry their supplies desert, taking most of the supplies with them.

The Explorers are faced with the dilemma of whether they should move on or try to get back to civilization. The group struggles on but is captured and held captive by hostile natives. Somehow the Explorers must escape and summon help, and hope that they can somehow determine what happened to Burton Monahan.