The Romy and Michele's High School Reunion star will play graphic designer Sara in the TNT drama.
In the show, her character gets pulled into the alien resistance after running into John Pope, played by Colin Cunningham.
Falling Skies tells the story about life after an alien invasion and stars Noah Wyle, Moon Bloodgood and Will Patton under director Steven Spielberg.
Also guest starring is Robert Sean Leonard. Season four has already begun production and will air in summer 2014.
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