Supergirl 4×21 “Red Dawn” Season 4 Episode 21 Promo – SUPERGIRL BATTLES RED DAUGHTER — Kara (Melissa Benoist) comes face to face with Red Daughter and the two engage in an epic battle. Determined to find a way to extract the Harun-El, Lena (Katie McGrath) turns to an unlikely source for help – Lillian Luthor (guest star Brenda Strong). Meanwhile, Alex (Chyler Leigh) realizes she’s missing parts of her memory, and Brainy (Jesse Rath), Nia (Nicole Maines) and J’onn (David Harewood) set out to track down aliens who have been abducted by Lex. Alexis Ostrander directed the episode with story by Lindsay Sturman and teleplay by Gabriel Llanas & Eric Carrasco (#421). Original airdate 5/12/2019.