"Parasite Lost" starts with James and Lena are at a lunch party — the former is upset that nationalist groups are stepping out in support of Guardian. Brainy drinks too many mojitos and ends up drunk. Kara introduces Nia to J'onn and Alex. After a quick nap, Brainy sobers up and notices Nia at the party and the two flirt.
Agent Jensen is doubled over in pain from the parasite Liberty inserted in his head. The two have a metahuman chained up and Liberty instructs Jensen to touch him. Upon the touching the meta, the parasite inside Jensen absorbs the meta's powers, killing the meta but giving said powers to Jensen.
At the DEO, Alex is speaking with Colonel Haley about Jensen. Haley encourages Alex to keep up the good work.
Kara and Nia go to the apartment of Amadei, a metahuman who they've heard can heal injured and disabled metahumans. Amadei finally grants Kara an interview in which he expresses his wants of being able to heal humans as well.
Jensen shows up at the National City Promenade. Instantly, alerts starting going off at the DEO and Alex assembles a strike team to confront Jensen. At the Promenade, a street performer is using his shapeshifting powers, of which Jensen wants to steal. Kara and Jensen begin fighting, but it's too late — Jensen's able to kill the shapeshifter and absorb his powers. Jensen gets away.
Alex briefs Colonel Haley on the situation, who orders that Kara stand down from the fight as a precautionary measure.
The next day, Kara and Nia are reading through the comments section on Kara's Amadei interview and they're full of negative comments, several including death threats against all metahumans.
J'onn's having a support group meeting with Amadei's helper rushes in asking for help. He and J'onn go to Amadei's apartment and find the healing metahuman in ailing health. Kara flies in and J'onn informs her that Amadei is dying.
With Casian's permission, J'onn reads Amadei's mind and finds out about Elizabeth Hawkings, the last person to see Amadei in a non-vegatative state. Kara and J'onn fly to Hawkings' home and while Kara distracts her, J'onn searches through her house.
J'onn accidentally bumps into Hawkins' mom, who screams. Elizabeth runs in the room and J'onn/Kara unveil that Elizabeth was the last one to see Amadei in good health. It's then that Elizabeth reveals that she's never seen Amadei because he's her deadbeat father.
James and Lena arrive at the dinner the Mayor of National City invited them to. Immediately upon their arrival, James is approached by Ben Lockwood. James informs Lockwood that he doesn't agree with Lockwood's anti-alien stance but the latter doesn't stand down — he continues trying to convince James that the vast majority of Americans are anti-alien.
Kara lets J'onn know that she regrets writing the glowing piece about Amadei earlier, disgusting about his actions against his daughter. J'onn isn't so sure the Hawkins' story is entirely accurate so the pair does some digging, and finds out that Amadei and his wife spoke more than his wife let on.
J'onn and Kara go back to the Hawkins residence, where Amadei's wife admits that he broke her heart, whih caused her to keep Elizabeth away from her. Mrs. Hawkins reveals that she's the one that cut out Amadei's amulet and sold it to a Child of Liberty she met on the dark web.
Team Supergirl realizes that Amadei's amulet was more than likely sold to Agent Jensen so that he could post as Amadei and still the powers of any metahumans that came to visit him.
The DEO narrows down a possible location of Jensen and converges on the spot. They enclose a several block radius in a dome that Brainy built. They arrive on scene and immediately begin fighting Jensen, who's trying to escape.
At the mayoral dinner, the mayor announces that a mass attack is happening in midtown and Lockwood speaks up, mentioning that James should go help out as Guardian. Jensen cracks a hole in the dome and realizing that he's more powerful than they thought, Alex calls in Kara.
The fighting stops and Jensen finds himself in a standoff with Kara and Alex. Alex tries convincing Jensen to turn himself in but the rogue DEO agent ends up taking out Amadei's amulet, presumably ending up killing himself.
J'onn reinserts Amadei's amulet and the alien is almost instantly healed. He's introduced to his daughter and two make amends.
Colonel Haley congratulates Alex on her work earlier in the day and reveals that Jensen is still alive, but braindead. She then reveals she's anti-alien, saying she helped launch the campaign to remove J'onn from power at the DEO.
Later that night, James and Lena are discussing the day's events. James tells Lena he needs to get to the bottom of the anti-alien nationalist movement. He tells her plans on infiltrating their system.3comments
Kara pitches a new idea to Nia which would feature a different National City alien each week, allowing people to get to know them.
Back at his hideout, Lockwood is upset over Jensen's death. James gives him a call and asks to meet up.