"Blood Memory" begins with troops in Kaznia training the Supergirl doppelganger. At the end of the training, the Kara clone is seemingly killed and when they go to revive her with a defibrillator, lightning comes out of her chest and zooms across the globe.
It then strikes an RV in National City that's used by local drug dealers. Some of their "inventory," is affected by the lightning. They sell some of the pills to customers and when one of the customers takes a pill, he starts morphing into a large alien.
At Kara's, the group has gathered for game night. They're talking about their favorite movies and when Alex is unable to guess Kara's, the latter is reminded of the memory-wiping events of the last episode.
The drug consumer is on a rampage through town and Alex gets an alert of it. She races out with Brainy and the DEO to stop the guy. Kara flies in as Supergirl and helps take the alien down. Kara calls Alex by her first name and the DEO agent reveals she wants to be called Director Danvers.
Kara's confiding in James the next day about the mind-wipe situation. Kara thinks it may have a bigger effect on her sister than initially thought. They're interrupted by a CatCo worker has a story pitch for James — she has a source within L-Corp that's uncovered a secret budget. The writer wants to follow the money trail, thinking it's covering up shady genetic testing.
Kara runs into Nia in the bathroom, who's upset that her flight for the weekend back home was cancelled. Kara offers to drive Nia home. The next day, the two begin the journey back to Nia's hometown. On the drive, Nia comes out as trans and reveals her parents were very supportive of her at a young age. She asks Kara to not tell her family about her dreaming powers.
At the DEO, Alex begins questioning the frat boys that took the drugs. After the interrogations, Brainy reveals that the drugs they took were infused with gamma radiation. Elsewhere, the drug dealers read comments on videos of the rampage and they realize they might be sitting on a goldmine with the rest of their supply. They decide to go on the road and sell the remaining drugs.
Nia's in a dream sequence, where she witnesses her mother crumble to dust. She wakes up just in time to arrive home. Once they get inside, Nia finds out the goblet she witnesses in the dream and accidentally breaking it, upsetting her sister.
The DEO finds out that more rages are happening across the city and they realize the drug dealers are peddling their supply. Alex is upset because she thinks she should be ahead of it and swears that something is missing from her mind. She calls J'onn in and tries to persuade him to scan her mind to find out what's wrong.
We find out that one daughter in each generation is Nia's family will get the dreaming powers. Her mother believes that Nia's older sister is the one to get the powers, but since they haven't flowered this late in life, the sister is getting upset. Nia reveals to Kara that she's going to try her mom that she's the one that got the powers and not her sister.
J'onn scans Alex's mind and lies to her that she's fine. J'onn convinces her that she might be so stressed because she doesn't have a partner at work.
Kara is interviewing Nia's sister for an article at work. Nia's sister reveals her wishes of becoming a crime-fighting superhero whenever she gets her powers.
At the DEO, Brainy's pretending to be a drug user and infiltrates the frat bros cell. It only takes a matter of seconds before he's able to get the names of the drug dealers that sold them the pills.
Nia sits down with her mother and asks her mother whether or not it's possible to transfer the dreaming powers to somebody else. Her mother explains that the dreaming power is non-transferrable, since it's in her blood. Nia's mom passes out and Nia enters her dream, where it's revealed Nia's mother is dying. Kara wakes Nia back up and they find out that her mother has passed away.
James arrives at Lena's office to speak with her about the mysterious accounting but finds out that Lena wants to train for game night instead.
The drug dealers stop because they have a buyer for the rest of their drugs. We soon find out the buyer is a group of Children of Liberty. They beat of the drug dealers and take the remaining pills, hoping to rage through the Harvest Fest in Nia's hometown to kill as many aliens as possible.
Brainy is able to track down the RV the dealers have been using. Alex assembles a group of DEO agents to track down the RV and they eventually arrive in Parthas, to find the two drug dealers tied up to a pole. One of the drug dealers reveals his little sister Roberta took the RV to track down the Children of Liberty.
In Parthas, the resident of the city begin gathering for a memorial for Nia's mother. Nia's sister is in the process of giving a eulogy when Nia has a vision of the aliens breaking in and causing destruction. Maeve — Nia's sister — continues the eulogy when one of the Children break in the barn. Nia pushes her sister out of the way, but the latter gets upset when she realizes that latter has the vision-seeking powers.
Robert arrives to help try taking down the Children of Liberty and an all-out battle breaks out between Kara, the Children of Liberty, Roberta, and the DEO. Alex nearly shoots an alien, but Kara uses laser-vision to shoot the gun out of Alex's hands.
Back at Nia's house, she and her sister have a fight over the powers. Things boil over when Nia's sister flies off the handle and tells Nia she's not a real woman.
Nia and Kara leave and start conversing about their sister's troubles. Kara eventually gets upset enough that she pulls over on the side of the road and flies away in front of Nia. She lands and reveals that she's Supergirl. Kara explains she knows exactly what Nia is going through with her sister troubles.
Back at CatCo, James calls in McKenzie and tells her that everything in her piece on L-Corp checks out as legal and that she was chasing a false lead. As McKenzie leaves, James appears visibly shaken, hinting that he lied to his employee about L-Corp.
When they arrive back in National City, Nia finally opens up the box her mom left her in the wake of her death to find that it's a superhero costume.0comments
J'onn's speaking with Kara at her apartment and reminds the Kryptonian that they'll need to end up supporting Alex no matter what happens between the DEO director and Supergirl. Alex arrives so that the group can watch T2 together.
The episode ends with a shot in Kaznia. The Supergirl doppelganger is apparently dead as a solider looks on. The soldier picks up a phone and tells somebody on the other that there's somebody he needs to speak with in America.