The insect traits Lex inherited from her mother, the evil Frau Mantiss, begin to take over her body, posing a threat to Storm City. Despite Rex's objections, Sgt. Agony orders both Leagues to bring Lex in, dead or alive. Robobot flees the city with a fugitive Lex to help her conquer her affliction.

In the Season 3 finale, Lex's insect half takes over completely, attacking League members and converting them to accomplices. The remaining heroes track Lex to a National Park, where she plans to start a conflagration that will destroy the entire planet.