Girl Of Steel Kara deals with the loss of Mon-El by focusing all her energy on being Supergirl and on the mysterious new threat against National City. Meanwhile, Alex confesses a secret to Maggie about their impending nuptials; Lena makes a bold move; and a citizen of National City possesses a mysterious connection to Kara.
Triggers Psi, a thief with psychic powers, attacks National City and is able to immobilize people by tapping into their worst fears. Meanwhile, James and Lena are at an impasse; and Samantha starts her new job at L-Corp.
Far From The Tree Eliza throws Alex and Maggie a wedding shower, which causes Maggie to reach out to her estranged father. Supergirl joins J'onn on a personal mission.
The Faithful Kara investigates a secretive 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 secret.
Damage When multiple children 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.
Midvale 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.
Wake Up 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. Samantha, eager for some understanding of the changes she has been experiencing, looks to her estranged mother, Patricia Arias, for answers.
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, The Ray, 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.