EXCLUSIVE: In his first post-House gig, Robert Sean Leonard has signed on for a five-episode arc on TNT’s sci-fi drama Falling Skies. Also set for a five-episode arc on the upcoming third season of Falling Skies is ER alumna Gloria Reuben, reuniting with her ER co-star, Falling Skies‘ leading man Noah Wyle.

Leonard, repped by WME and manager Danny Sussman, will play Roger Kadar, PhD, an obsessive but gifted scientist who runs Charleston’s power grid and lives underground with his pet rats. The children of New Charleston, intrigued by his cool science toys and unusual pets, eventually dub him “The Rat King.” For the past eight seasons, Leonard played Gregory House’s (Hugh Laurie) best friend and moral compass Dr. James Wilson on the Fox medical drama. Following his arc on Falling Skies, he is likely to return to series full-time as he is already fielding interest for pilots.

Reuben, repped by APA and manager Estelle Lasher, will play Marina Perlata, an aide to Wyle’s Tom Mason, who has been one of the leaders from the human resistance movement against an invading alien force. Attractive and a very put together woman, Marina is extremely intelligent and her political knowledge and experience could prove extremely helpful to Tom. This marks Reuben’s return to TNT where she starred in the legal drama Raising The Bar. She will next be seen in Lincoln.