|Season 3, Episode 17 (57)|
|Nova Day||The House of Zod|
PART 3 OF 8: ALEX TAKES COMMAND OF EARTH'S DEFENSE- When J'onn is incapacitated, Alex steps up as interim director of the DEO when Brainiac attacks Earth, ultimately learning the hard way that the Phantom Zone still exists. On New Krypton, Lesla-Lar works to save the lives of Dru-Zod, Kal, and Karen while Kara and Astra pursue Ral-Dar.
- Melissa Benoist as Kara Danvers/Supergirl
- Chyler Leigh as Alex Danvers
- Katie McGrath as Lena Luthor
- Laura Benanti as Alura Zor-El/Astra In-Ze
- Zachary Quinto as General Dru-Zod
- Tyler Hoechlin as Kal-El & Cyborg Superman
- Odette Annable as Samantha Arias/Reign
- Jenna Dewan as Lucy Lane/Superwoman
- with Claire Holt as Karen Starr
- and David Harewood as J'onn J'onzz/Martian Manhunter
Special Guest StarsEdit
- Jon Cryer as Lex Luthor
- Dean Cain as Brainiac
- Michael Rosenbaum as Lex Luthor (Earth-30)
- Sarah Douglas as Jindah Kol Rozz
- Chris Wood as M'On-El
- Mehcad Brooks as James Olsen/Guardian
- Floriana Lima as Maggie Danvers
- and Peter Facinelli as Max Lord
- Amy Acker as Brainiac
- Brenda Strong as Dr. Lillian Luthor
- Tracy Spiridakos as Lesla-Lar
- Dianna Agron as Major Raya Zod-El
- Amy Jackson as Imra Ardeen/Saturn Girl
- Glenn Morshower as General Sam Lane
- Minka Kelly as Lois Lane
- Gregg Henry as Ral-Dar
- Jesse Rath as Brainiac 5
- Chad Lowe as Thomas Coville
- Andrea Brooks as Eve Teschmacher
- Tamzin Merchant as Lyra Strayd
- Lauren German as President Veronica Banks
- Emma Tremblay as Ruby Arias
- Robert Gant as Brainiac
- Chris Browning as Ben Krull/Reactron
- Briana Venskus as Agent Susan Vasquez
- Wallis Day as Junior Magistrate Nyssa-Vex
- with Emmy Rossum as Zaora Dru-Zod
- and Billy Zane as LX-13
- Antagonists: Brainiac, Sam Lane, Lex Luthor
- This episode is Alex-centric.
- 8th episode this season to feature all main characters.
- This episode is concurrent with Nova Day and The House of Zod. It occurs during the afternoon of June 24, 2020.
- James was last seen in Brave Enough.
- Krull was last seen in Fight or Flight.
- This episode is notable for featuring nearly every significant living character that has appeared on the show.