|Season 3, Episode 18|
|Nova Day||The House of Zod|
The Swarm is the eighteenth episode of Supergirl Season 3 and the 60th episode overall. It is the third part of the 5-part TRIAL storyline, focusing on the political strife on New Krypton.
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, Lara and Savage work 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
- Jeremy Jordan as Winslow Schott
- Katie McGrath as Lena Luthor
- Laura Benanti as Alura Zor-El/Astra In-Ze
- Tyler Hoechlin as Kal-El
- Floriana Lima as Maggie Danvers
- Zachary Quinto as General Dru-Zod
- 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
- Dean Cain as Brainiac
- Michael Rosenbaum as Lex Luthor (Earth-30)
- Chris Wood as M'On-El
- Mehcad Brooks as James Olsen/Guardian
- with Peter Facinelli as Max Lord
- and Calista Flockhart as Cat Grant
- Amy Acker as Brainiac
- Brenda Strong as Lillian Luthor
- Tracy Spiridakos as Lesla-Lar
- Dianna Agron as Raya Zod-El
- Paige Turco as Lara Lor-Van
- Amy Jackson as Imra Ardeen/Saturn Girl
- Glenn Morshower as General Sam Lane
- Minka Kelly as Lois Lane
- Gregg Henry as Ral-Dar
- Jess Rath as Brainiac 5
- 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
- and Billy Zane as Lex Luthor
- Antagonists: Brainiac, Sam Lane, Lex Luthor
- This episode is Alex-centric.
- 8th episode this season to feature all main characters.
- James was last seen in Brave Enough.
- Krull was last seen in Fight or Flight.