Magnum accuses Higgins of being Robin Masters, saying that the voice of Masters is an actor that sounds like Orson Welles. In an earlier episode involving a treasure hunt, Magnum states that he accompanied Masters on a trip to this remote location so that he could work out the locations for a book about buried treasure. Despite the clues having been destroyed, he worked out the locations by reading the book and retracing the steps that he and Masters took. Either his companion was Masters, or an extremely convincing actor who took such good notes that Masters could imagine what things looked like, which is wildly improbable. Odds are that if the voice of Robin Masters
Orson Welles had not passed away during the sixth season, the Higgins as Masters thread - one that runs to the end of the series - would not have been developed.