"Strange that you boys should be talking about the 'Lost Expedition.'" "Oh, hello, Dad. Why strange?" "Because I have just come from a conference with a man who knows all there is to know about it. And he was telling me--." Mr. Hampton advanced from the doorway into the sitting room, and looked at the faces of the three boys in turn. They were his son, Jack, and the latter's chums, Bob Temple and Frank Merrick, who together had gone through many adventures related in other books of "The Radio Boys" series. It was the sitting room of a suite in a Seattle hotel. Here the four, arriving from South America, after finding and losing "The Enchanted City of the Incas" as told of in "The Radio Boys Search for the Incas' Treasure," were ensconced on their way to their Long Island homes.