- "I spent the last 300 years trying to repent for having fled Mars, only to find out that is the least of my sins."
- —J'onn J'onzz on remembering his past with Malefic J'onzz
- Melissa Benoist as Kara Danvers/Supergirl
- Mehcad Brooks as James Olsen/Guardian
- Chyler Leigh as Alex Danvers
- Katie McGrath as Lena Luthor
- Jesse Rath as Querl Dox/Brainiac 5
- Nicole Maines as Nia Nal
- Azie Tesfai as Kelly Olsen
- Andrea Brooks as Hope
- Julie Gonzalo as Andrea Rojas
- Staz Nair as William Dey
- David Harewood as J'onn J'onzz
Special guest star
- Marcus Aurelio Jr. as Martian Child #3
- Cassandra Cavalli as Counter Lady
- Hunter Dong as Coffee Cart Barista
- Ava Frica as Martian Child #4
- Marcello Guedes as Young Malefic
- Eric Gustafsson as Receptionist
- Babak Haleky as Janitor
- Sean Hewlett as Franklin
- Balinder Johal as Old Lady
- Larry MacDonald as Strange Man
- Marc-Anthony Massiah as Dr. Andrew Stern
- Malcolm Masters as Dr. Niles Jarrod
- Ethan Matute as Martian Child #2
- Antonio Ndala as Young J'onn
- Dominique Robinson as Young Adult Malefic
- Sasha Rojen as Martian Child #1
At a night club William Dey approaches a man and once again demands he reconsider working together. The man again declines and leaves to go talk to a blonde with tattoos. They find themselves making out in the bathroom, only for her tattoos to come alive, crawl inside his body and kill him.
Kara, Alex, James, and Kelly are all walking together, presumably on their way to work. James and Kelly take off, while Kara and Alex continued discussing Kara's anxiety about having lunch with Lena for the first time after telling her she is Supergirl. Alex insists everything will be fine. While at work Andrea Rojas wants a sexy story of a murder, when coming across billionaire, Niles Jarrod who died at a club, she waves it off as nothing important. Kara and William find themselves in a verbal altercation, and Kara uses her Super Hearing and finds out he is nervous. William tells the room he has already looked into the story, and there is nothing there. Afterwards, Kara confronts William outside about why he was lying. He blows her off as being paranoid.
Lena is in her office trying to untangle the DNA in order to help manipulate it, still on her quest to help the human race. But unable to find the answers, Hope accesses Eve Teschmacher's memories to reveal the answers are in Lex's old journals. Knowing they are locked away and she can't get to them, she decides to incorporate Supergirl into her plan. Kara arrives at Leno's office to have lunch, having flown over to Paris, Milan, Dublin to pick up her favorite food. Insisting she didn't need to do that, Lena brings up her a-legend nightmare she's been having. Telling Kara the only thing that brings her pieces reading Lex's journals, unfortunately, they are locked away. Kara immediately volunteers to get them for her friend.
Nia Nal is getting ready for the morning while Brainy continues to read her poetry much to her annoyance. This has been going on for days, and she has yet to say anything to him. She goes to meet J'onn J'onzz at his office, where they begin to discuss his missing memories. He makes her tea to help them mentally reconnect before going inside his mind. There everyone she sees as in human form, so her mind can understand what's happening. They see J'onn playing with his younger brother Malefic J'onzz, but it becomes clear he is unable to connect to the hive-mind. Their father deciding he is a danger locks him away. He grows older and resentful and eventually sides with the White Martians. His father, M'yrnn J'onzz is devastated and erases him from both their memories. Coming out of the dream-like memory J'onn condemns his father for doing something so horrible. Because death is not final for their kind, but erasing a memory is. Back at home, Nia is woken from a nightmare, having discovered the rest of the memory. She immediately finds J'onn, and he agrees to watching the rest of his memory. It reveals it wasn't their father who erased their minds, but J'onn, after he saw how destroyed his father was. J'onn is absolutely devastated at what he did. Back at Nia's she finally confronts Brainy about his obsessive affection towards her. She tells him it's too much, visibly hurt Brainy leaves.
At the DEO Supergirl, Alex, and James discover that military officer Caroline O'Connor is the new host for the Aurafacian. Supergirl goes to her apartment but is shot with web-shooters against a wall. James breaks through the door and is able to fight her off before he is attacked with one of her tattoo spiders. Supergirl takes them both back to the DEO. James fully recovers, and Brainy goes to work looking into the information on the USB stick Supergirl found at the apartment. They come to the realization that Dr. Andrew Stern at National City General Hospital is in danger. They immediately find him at the hospital, and though he is still attacked by the tattooed spiders, they are able to save him. Supergirl and Caroline have a physical hand-to-hand fight before Supergirl wins by knocking her off the overhang. Before they can question her she is immediately killed by an unknown moving blur.
Malefic sneaks into Kelly's apartment and looks over photos. He finds a photo of her with an old friend and shape-shifts into Pete Andrews. He then meets her at her new office, under the guise of needing help. She agrees to meet with him after work. Over dinner, she again finds herself agreeing to bring him into her laboratory to run some quick tests. After Malefic finds out what he wants he immediately attacks Kelly. Controlling her mind, before forcing her to stop herself, J'onn arrives to fight his brother. Malefic escapes into the rest of the building, but Kelly is still able to see him even when he shapeshifts. Knowing this would make her a target, everyone agrees to send her into hiding. James volunteers to drive his sister, and Alex makes him promise to tell no one, not even her. Supergirl having already broken into the government police station to steal Lex's books, also is able to give one of Lex's transmatter portal watches and gives it to James before he leaves. Supergirl finds Lena at her apartment to give her Lex's journals. Down in Lena's basement after reading over them she is unable to decipher them. Though Hope is and soon has the answers ready for her. Meanwhile, William is seen sitting on a park bench. A man passes him a rolled-up newspaper with money inside of it.
- When James and Kelly are leaving, the license plate reads "590 WUG". This is the same license plate used for the get-away car to kidnap Tanya Spears in the third season episode "".
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