Buck Rogers in the 25th Century: 2x6

Mark of the Saurian

The Saurians plot to destroy the Searcher and start a galactic war by infiltrating the starship and a space station in human disguise. Only Buck, who has contracted a strange virus, is able to see the true form of the Saurians, but no one believes him. When the Suarians realize that Buck is a threat to them, he becomes the target of their assassination attempts.