Original air date: 10/09/2017 Runtime: 42:21 min. In the season three premiere, 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 (recurring guest star FLORIANA LIMA) about their impending nuptials. A citizen of National City has a mysterious connection to Kara, and Lena makes a bold move.
Original air date: 10/16/2017 Runtime: 42:23 min. Psi (guest star YAEL GROBGLAS), 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 (new series regular ODETTE ANNABLE) starts her new job at L-Corp.
Original air date: 10/30/2017 Runtime: 42:13 min. Kara investigates a secretive new group whose leader, Thomas Coville (guest star CHAD LOWE), has a mysterious connection to Supergirl. Meanwhile, Samantha feels like she’s letting her daughter, Ruby (recurring guest star EMMA TREMBLAY) down; and J’onn confesses an old secret.
Original air date: 11/06/2017 Runtime: 42:21 min. When multiple children get sick from lead poisoning, Morgan Edge (guest star ADRIAN PASDAR) 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.
Original air date: 11/13/2017 Runtime: 42:24 min. 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 who that traumatic experience brought the Danvers sisters closer together. IZABELA VIDOVIC plays Young Kara and OLIVIA NIKKANEN plays Young Alex in flashbacks.
Original air date: 11/20/2017 Runtime: 42:14 min. When Winn and the team discover 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 (recurring guest star CARL LUMBLY). Samantha, eager for some understanding of the changes she has been experiencing, looks to her estranged mother, Patricia Arias (guest star BETTY BUCKLEY), for answers.
Original air date: 11/27/2017 Runtime: 42:15 min. The epic four-way crossover with Arrow, Supergirl, The Flash and DC’s Legends of Tomorrow begins. Barry Allen (guest star GRANT GUSTIN) and Iris West’s (guest star CANDICE PATTON) 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 (guest star EMILY BETT RICKARDS), and Alex Danvers to take on their most formidable villains yet. Earth’s mightiest heroes – Green Arrow (guest star STEPHEN AMELL), Supergirl, The Flash and White Canary (guest star CAITY LOTZ) – lead their teams into battle to save the world.
Original air date: 12/04/2017 Runtime: 42:07 min. 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. 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.
Original air date: 01/15/2018 Runtime: 42:21 min. 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 Super Heroes to try to stop her.
Original air date: 01/22/2018 Runtime: 42:21 min. As Reign 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, 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.
Original air date: 01/29/2018 Runtime: 42:18 min. 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.
Original air date: 02/05/2018 Runtime: 42:22 min. 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.