The synopsis says Supergirl will be aiming to "capture" Mercy for a currently undisclosed reason, though it will likely relate to the events of the premiere. Despite its mention of Mercy, the synopsis gives no indication that Otis will also appear in the episode. The synopsis also teases "a precarious situation" for Brainiac-5 and new character Nia, while teasing Alex's advancement at the DEO.
CHAOS IN NATIONAL CITY — A shocking revelation causes chaos in National City. Supergirl (Melissa Benoist) sets out to capture Mercy Graves (guest star Rhona Mitra), while Alex (Chyler Leigh) takes control at the DEO. Back at CatCo, Kara decides to write an investigative story on Mercy and asks Lena (Katie McGrath) if she can interview her as Mercy has ties to the Luthors. Meanwhile, Brainy (Jesse Rath) meets Nia (Nicole Maines) and the two end up in a precarious situation. Harry Jierjian directed the episode with story by Dana Horgan and teleplay by Maria Maggenti & Daniel Beaty (#402). Original airdate 10/21/2018
Supergirl Season 4 will see the departure of series regular Chris Wood, who plays Mon-El, and Jeremy Jordan, who plays Winn Schott, being reduced to a recurring role. Jesse Rath’s Brainiac-5 will be upgraded to a series regular for Season 4. Several new actors will join the CW show, including Nicole Maines as the first transgender superhero in DCTV history and former Tron star Bruce Boxleitner as the Vice President of the United States.
Starring Melissa Benoist as Kara Danvers, David Harewood as Martian Manhunter, Mehcad Brooks as Jimmy Olsen, and Chyler Leigh as Alex Danvers, Supergirl returns for its fourth season on Sunday, Oct. 14, at 8 pm ET/PT on The CW.