Supergirl 3×13 “Both Sides Now” Season 3 Episode 13 Promo – THE DEO CAPTURES ANOTHER WORLDKILLER – The DEO captures a second Worldkiller, Purity (guest star Krys Marshall). Supergirl (Melissa Benoist) and Alex (Chyler Leigh) use very different methods of interrogation with Purity in the hopes of finding out how to defeat Reign (Odette Annable). However, Purity escapes and attacks the city’s subway tunnels. Meanwhile, J’onn (David Harewood), Winn (Jeremy Jordan) and Mon-El (Christopher Wood) band together to fix the Legion ship. Jesse Warn directed the episode written by Jessica Queller & Paula Yoo (#313). Original airdate 2/5/2018.