“Bunker Hill” starts with Nia having a nightmare of sorts — she has powers that allow her to see things before they happen while dreaming. At work, Kara confronts Nia about lying to everyone at Thankgiving about having narcolepsy.
Ben Lockwood returns home to his wife informing him of a former college classmate showing up. It’s revealed Manchester Black arrived to the house to harm Lockwood. J’onn uses his telepathic link to warn Manchester not to do anything. Lockwood’s wife leaves the room and Manchester pulls a gun out on Ben.
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Kara arrives to Nia’s house to talk to her about her powers. There, Nia reveals she’s from a planet called Naltor. Kara calls in Brainy, who also reveals he’s an alien. There, Brainy’s able to use his powers to send Nia to her dream state, where she continues to see the woman in pain from earlier.
Nia wakes up and tells the group they need to go to Collinwood High School because that’s where the troubled woman is.
Back at the Lockwood residence, Manchester has now pulled a dagger out, holding both of the Lockwoods hostage accusing Ben of being Agent Liberty. J’onn tries to stop Manchester through telepathic means again, but he’s unsuccessful.
Nia arrives at Collinwood with Kara and Brainy and we see one of the other Liberty agents with an alien-sniffing dog. Kara instantly picks up his identity and realizes he’s with two other agents. Kara devises a plan where she takes care of the agents while Brainy distracts Nia. Kara thinks if they kidnap her, they could lead her straight to the woman in trouble.
Kara approaches the group and a van pulls up to throw her in. Nia looks down the street and notices the commotion. She runs back and Brainy is forced to follow. The agents kidnap all three of them and take them to the agents’ hideout.
There, the agents get nervous and try shooting Nia, who sees the event coming. She’s able to use the bullet shot to bust her out of the handcuffs and she helps the other two out. Chaos ensues although the trio is able to quickly subdue the agents.
Ben takes Manchester and his wife to the basement of the Lockwood residence and Ben reveals to his wife that he is, in fact, Agent Liberty.
Kara does some investigating and realizes they’re at Lockwood Family Steel. The trio quickly draws a line to Ben Lockwood being Agent Liberty and Kara calls Alex to see if she can confirm. Alex has a Child of Liberty in custody and after a quick interrogation, he confirms that Lockwood is Agent Liberty.
Manchester makes Ben suit up in his Agent Liberty costume and starts beating him up for being behind the murder of Fiona. J’onn uses his telepathy again and Manchester says the only way he’ll stop is if J’onn kills him. J’onn refuses. Manchester and Ben continue their fight and Ben eventually busts through the storm door, leading Manchester on a chase.
Kara leaves the steel factory to help Manchester, but she has trouble locating them since they’re no longer at the Lockwood residence.
Brainy and Nia start investigating the factory itself and Nia realizes that this place is, in fact, the location from her dreams.
Ben leads Manchester straight to the steel factory. Manchester’s about to shoot Lockwood when Kara flies in and stops him. The two debate over killing Lockwood. Eventually, Manchester is able to pour nth metal on Kara, adhering her to the floor.
Lockwood’s wife arrives and distracts Manchester. Ben’s nearly about to kill Manchester when Supergirl breaks free and stops him, saving Mrs. Lockwood from plummeting to her death in the process. National City police arrive to arrest Lockwood and Manchester for their crimes.
Kara flies back to the DEO and is surprised by the presence of President Baker. There, he informs Kara that she needs to put her country first and reveal her secret identity. Kara refuses to reveal that information and Baker relieves her from DEO duty.
Massive protests in defense of Lockwood begin to form outside of the country jail and CatCo Media.
The episodes ends with the Monitor killing all of the heroes on Earth-90. John Wesley Shipp’s Flash is able to escape.