The Flash and Cisco Come to National City in Supergirl's "Medusa" Synopsis

As Earth-1 ramps up for Invasion!, The Flash and Cisco Ramon will come to Supergirl for help in "Medusa," the November 28 episode of Supergirl.

Before that, though, it's not exactly a slow week, as Alex decides to come out to her mother, Winn and James stand on the brink of making a major decision about The Guardian, and Supergirl enlists the aid of an unexpected ally in her battle with Cadmus.

You can check out the official synosis below:

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.

Arrow, The Flash, and Supergirl will cross over with DC's Legends of Tomorrow later this month in "Invasion!" a three-part crossover that starts in the final moments of an episode of Supergirl and then plays through the other series. Based on the 1988 comic book event miniseries Invasion! from Keith Giffen, Bill Mantlo, Todd McFarlane, Bart Sears, and more, EW confirms that it will closely track the plot of that storyline: aliens will be assembled by The Dominators and descend on Earth to bring an end to the "threat" of Earth's burgeoning metahuman community.

In the TV version, rather than assembling a loose alliance of dangerous alien races, the Dominators will apparently be mind-controlling the aliens that join them. That could mean that even the heroes might be forced to take one another on at some point in the story.

Supergirl airs Mondays at 8 p.m. ET/PT; The Flash on Tuesdays at the same time; Arrow on Wednesdays and DC's Legends of Tomorrow on Thursdays. All four series air on The CW. The "Invasion!" crossover will air beginning November 28.