Season 3 Episodes
01: Girl of Steel
Kara deals with the loss of Mon-El by focusing all her energy on being Supergirl and the mysterious new threat against National City. Alex confesses a secret to Maggie about their impending nuptials. A citizen of National City has a mysterious connection to Kara, and Lena makes a bold move.
Psi (guest star Yael Grobglas from "Jane the Virgin"), a thief with psychic powers, attacks National City. Able to immobilize people by tapping into their worst fears, Psi proves a formidable opponent for Supergirl. Meanwhile, James and Lena are at an impasse, and Samantha starts her new job at L-Corp.
03: Far from the Tree
Eliza (guest star Helen Slater) throws Alex and Maggie a wedding shower, which causes Maggie to reach out to her estranged father (guest star Carlos Bernard). Supergirl joins J’onn on a personal mission.
04: The Faithful
Kara investigates a secrective new group whose leader, Thomas Coville has a mysterious connection to Supergirl. Meanwhile, Samantha feels like she's letting Ruby down, and J'onn confesses an old secrect.
When multiple childre get sick from lead poisoning, Morgan Edge points the finger at Lena and blames her creation of the lead bomb she made to save National City from the Daxamites. While Lena knows she never intended any harm, she fears there may have been a flaw in her design, leaving her responsible. Kara teams up with Samantha to clear Lena's name, but it turns out to be harder than they thought. Meanwhile, Alex and Maggie make a crucial decision about the future of their relationship.
Kara and Alex head home to Midvale for a little R&R. While there, Kara recalls a painful memory of a childhood friend's death and how that traumatic experience brought the Danver sisters closer together.
07: Wake Up
When Winn and the team discovered an alien ship has crash landed deep underwater beneath National City, Kara/Supergirl is called in to investigate. Meanwhile, Hank attempts to bond with his father, Myr’nn. Samantha, eager for some understanding of the changes she has been experiencing, looks to her estranged mother, Patricia Arias for answers.
08: Crisis on Earth-X, Part 1
Barry and Iris’s wedding brings the gang together, but things go awry when villains from Earth-X attack the ceremony. All of the superheroes band together with help from their super friends like Citizen Cold (guest star Wentworth Miller), The Ray (guest star Russell Tovey), Felicity Smoak, Iris West and Alex Danvers to take on their most formidable villains yet. Earth’s mightiest heroes—Green Arrow, Supergirl, The Flash and White Canary—lead their teams into battle to save the world.
Supergirl investigates a mysterious symbol popping up all over National City, tracing its origins back to an ancient prophecy and the mark of the World Killer, Reign (Odetee Annable). Meanwhile, the tension between Lena and Morgan Edge continues to build, causing James to step in and offer up some protection, and possibly igniting a spark in the process.
10: Legion of Super-Heroes
Struggling to heal from her injuries inflicted by Reign, Supergirl remains in a dreamlike state, unable to be reached. Mon-El recruits one of the Legion members, Brainiac-5 (guest star Jesse Rath), to try to bring her back. Meanwhile, Reign continues her rampage on the city so the DEO teams up with the Legion of Superheroes to try to stop her.
11: Fort Rozz
As Reign (Odette Annable) continues to terrorize the city, Supergirl teams up with Saturn Girl (guest star Amy Jackson), and the two recruit Supergirl’s former enemies, Livewire (guest star Brit Morgan) and Psi (guest star Yael Grobglas), to form a team for a mission to Fort Rozz to recover a prisoner who has information on how to defeat Reign once and for all. Meanwhile, Alex babysits Ruby (guest star Emma Tremblay).
12: For Good
Someone tries to kill Morgan Edge and he barely survives. He accuses Lena of being behind the attempt and vows to destroy her. When Lena fears her hatred for Morgan will take her to the Luthor dark side, Kara steps in to help her friend. Meanwhile, after Sam realizes she’s losing time, she confides in Alex who decides to run some medical tests to see if she can find out what’s going on with her new friend.
13: Both Sides Now
The DEO captures a second Worldkiller, Purity (guest star Krys Marshall). Supergirl and Alex use very different methods of interrogation with Purity in the hopes of finding out how to defeat Reign. However, Purity escapes and attacks the city’s subway tunnels. Meanwhile, J’onn, Winn and Mon-El band together to fix the Legion ship.
14: Schott Through the Heart
When Winn’s father dies, his estranged mother, Mary (Oscar-nominated guest star Laurie Metcalf), reappears trying to reconnect and to explain why she abandoned him all those years ago. Winn is too embittered from his rough childhood to forgive her but when a copycat Toyman attacks, the two must work together to stop him. Mon-El tells Kara something important about the Worldkillers, and Alex becomes suspicious of Myr’nn’s recent behavior.
15: In Search of Lost Time
When Myr’nn (guest star Carl Lumbly) inadvertently causes psychic disturbances at the DEO, Supergirl must work with J’onn to contain the resulting chaos. Meanwhile, Mon-El begins training Kara in fighting techniques he’s learned in the future for battling Worldkillers.
16: Of Two Minds
Supergirl and Imra (guest star Amy Jackson) have different ideas on how to stop the third Worldkiller, Pestilence. However, when both Alex and Winn are seriously injured by Pestilence, Supergirl and Imra team up to stop the destruction.