Helen Slater returns to Supergirl as Eliza Danvers and the four-show “Invasion!” crossover is set up in the November 28 episode of the show, and The CW has now released an official description for it!
The episode is called “Medusa” and the write-up can be found below. If you want descriptions for all four shows in the crossover, you can find them at KSiteTV.
A NIGHT OF CONFESSIONS; THE EPIC SUPERHERO CROSSOVER KICKS OFF TONIGHT — Eliza (guest star Helen Slater) comes to town to celebrate Thanksgiving with her daughters. Alex (Chyler Leigh) decides it’s time to come out to her mother; Kara (Melisa Benoist) is shocked when Eliza suggests Mon-El (Chris Wood) has feelings for her, and Winn (Jeremy Jordan) and James (Mehcad Brooks) consider telling Kara the truth about the Guardian. Meanwhile, CADMUS unleashes a virus that instantly kills any alien in the vicinity so Kara enlists an unexpected ally – Lena Luthor (Katie McGrath). The epic superhero crossover kicks off tonight when Barry Allen (guest star Grant Gustin) and Cisco Ramon (guest star Carlos Valdes) seek Kara’s help with an alien invasion on their Earth. Stefan Pleszczynski directed the episode written by Jessica Queller & Derek Simon (SPG208). Original airdate 11/28/2016.