When the Feminum Mystique begins, Steve and Diana head to an airbase so Steve can test fly a new-fangled jet aircraft prototype. But Nazi spies, led by John Saxon (better known to horror movie fans from A Nightmare On Elm Street and Tenebre) steal the fighter and try to fly it back to Germany. But no sooner than the plane is aloft than it is blown up by the Americans, who feared something like this might happen and had this self-destruct plan set up. Although the spies are denied the fighter, they still radio back reports of Wonder Woman, who fought off the German commandos at the airbase. Intrigued, the German High Command orders further investigation of this Wonder Woman.

Meanwhile, on Paradise Island, the Queen gets lonely for her daughter Diana. So she sends Drusilla, her youngest daughter, to America to fetch Diana and bring her home. When they meet up in Washington, Diana tries to convince Dru that she is still needed here. The Nazi spies who tried to steal the plane now kidnap General Blankenship, Diana and Steve's boss, as a way to flush Wonder Woman out. But Drusilla, who was with Blankenship when he was abducted, decides to rescue him herself as Wonder Girl. But in her attempt to free him, Wonder Girl winds up getting captured by the Nazis herself. But the irony is that the Nazis think they actually have Wonder Woman. When they trick Wonder Girl into telling them the location of Paradise Island, Wonder Woman is forced to return home to defend it against a German invasion.

The Feminum Mystique is a fun two parter that has become special for its casting of actress Debra Winger as Drusilla. Winger would go on to become a top Hollywood actress in the 1980s, starring in such films as An Officer And A Gentleman, Terms Of Endearment, and Urban Cowboy. Here she plays Drusilla as a sweet young girl who is even more innocent than Diana. She retuned as Drusilla/Wonder Girl later in the first season in the episode Wonder Woman In Hollywood. Another interesting bit of casting in The Feminum Mystique occurred when Carolyn Jones was cast as Diana/Wonder Woman's mother, Queen Hippolyta. Jones replaced Cloris Leachman, who first played the part in the series' pilot episode. Carolyn Jones is better known as Morticia from the original Addams Family TV series.