Supergirl Recap With Spoilers: The Darkest Place

The episode opens with Supergirl and J'onn fighting. Supergirl asks why he's doing this, but J'onn just responds that it's time for her to die. 

The show immediately flash backs to Kara, Winn, Jimmy, and Alex visiting the (still unnamed) alien bar. Jimmy and Kara discuss Guardian's latest heroics, but Kara still doesn't trust him. Alex mentions that Guardian seems to be working with someone, as Guardian is always one step ahead. Supergirl brings up that her cousin worked with a vigilante once (BATMAN ALERT) and claims that vigilantes are nuts. Maggie pulls Alex aside and asks if things are okay between them, but Alex plays it cool. When Alex gets back to the table, she asks where Mon-El is, but Kara says he's probably just shacked up with some girl.

But Mon-El isn't with a girl, he's trapped inside a cage at Cadmus. Although he manages to beat up a guard and steal his keys to escape the cage, Mon-El stops when the head of Cadmus (Lena's mom) shows up with J'onn in tow. She says that if she tries to escape, she'll kill J'onn, so Mon-El agrees to stay at Cadmus.

But J'onn is actually at the DEO and is thrilled to see M'gann when she stops by with a Martian brew to help him recover from last week's attack and transfusion. He suddenly hallucinates and sees his family, but plays it off as if nothing were happening.

Guardian grabs a fleeing burglar and strings him up on a street light for the police. After they drive away, a second vigilante arrives and shoots the burglar in the face. 

Jimmy arrives at work the next day and finds out the Guardian was set up for the murder of the burglar. He tries to convince Snapper that the Guardian didn't kill him, but Snapper says that Jimmy is biased. Winn shows up to freak out and says they need to shut down Guardian, but Jimmy says they can lure out the copycat at a drug bust that night.

At the DEO headquarters, J'onn admits to Supergirl that he's been hallucinating. Supergirl suggests that it's because he's feeling guilty because he's found M'gann and isn't alone anymore.

Sure enough, the Guardian's copycat vigilante shows up at the drug bust and kills one of drug dealers before confronting Guardian. The copycat wants to keep the streets safe too, but Guardian says that he doesn't kill. The copycat flees right as police arrive, leading to the police opening fire on Guardian.

When Supergirl flies towards the firefight, Cadmus interrupts her via a frequency that only Supergirl can hear (a callout to the first Superman movie). The head of Cadmus says that they have Mon-El and invites Supergirl to rescue him. 

When Supergirl flies into the Cadmus headquarters, J'onn...or at least someone who she thinks is J'onn is there to great her. Supergirl quickly realizes that he's actually Hank Henshaw, who survived the botched DEO meeting after all. Henshaw and Supergirl immediately start fighting, but it seems that Henshaw has gotten some cybernetic enhancements during his time with Cadmus. Even though Supergirl burns off half his face, Henshaw quickly gets the upper hand.

When Alex starts asking about Kara at the DEO, Winn says that she's probably at CatCo. Winn makes a comment about Guardian, Alex susses out that Winn is involved with Guardian and quickly gets him to crack. Alex threatens to call Kara, but Winn convinces her to let Jimmy clear his own name. 

Supergirl wakes up in the cage next to Mon-El. She can't escape, because the bars are made from Nth Metal. 

Alex asks Maggie to lay off of Guardian. When Maggie presses Alex for details, Alex snaps at her and says they aren't friends, because Maggie pushed her to come out and then rejected her. 

Back at the DEO, J'onn has another hallucination...this time that one of his co-workers is a White Martian. Alex convinces him to stand down, and J'onn orders her to give him some medical tests.

The head of Cadmus confronts Supergirl, and Supergirl recognizes her from Lena's office. Supergirl discovers that the head of Cadmus is Lillian Luthor, Lex and Lena's mother. Lillian claims that Superman convinced the world that Lex was evil and took up his cause. Lillian explains that she brought Supergirl in because she needs to "human" for a little bit by using her solar flare ability. Lillian brings in a helmet designed to contain Supergirl's heat blast and threatens to kill Mon-El if she doesn't comply. After shooting Mon-El in the leg, Supergirl reluctantly agrees. Supergirl uses the solar flare, draining her powers completely. Lillian orders her men to take Supergirl to an operating room and begins drawing her blood into a tube. 

Winn pieces together that the copycat killer is targeting criminals who have been freed on technicalities. He says that the copycat is probably Phillip Karnowsky, an ex-Navy SEAL whose wife was killed. When the killer went free due to a mistrial, Winn thinks that Karnowsky took matters into his own hands.

Alex and J'onn test J'onn's blood and discovers that something is attacking his blood cells. J'onn has seen this before and immediately rushes off to confront M'gann. J'onn says he knows that M'gann is a White Martian, but M'gann says she's not like the others. M'gann claims she couldn't stand watching her race exterminate the Green Martians and tried to save as many as she could. J'onn is still upset and forces M'gann to reveal her true form. 

Cadmus throws Supergirl back in her cage after taking her blood. Supergirl admits to Mon-El that she's scared, and Mon-El tries to tell her something about the destruction of Daxam. Before Mon-El can say anything, Jeremiah suddenly shows up and lets Supergirl and Mon-El out of their cages. After pulling the bullet out of Mon-El's leg, Jeremiah leads them to safety but stays behind.

J'onn starts fighting M'gann, claiming he wants to avenge the death of his species. When J'onn throws M'gann to the ground, she transforms back into her human form and says that if he's going to kill her, she wants to die as who "she wants to be."

Guardian finds Karnowsky right before he kills another criminal. After a lengthy fight, Guardian gets the upper hand and throws Karnowsky right into the waiting arms of Maggie and Alex. Maggie lets Guardian get away before NCPD backup arrives. 

Alex rushes into the DEO headquarters after hearing the news about Supergirl. Supergirl tells Alex about Jeremiah, but Cadmus abandons their headquarters before Alex and the DEO can rescue him.

J'onn has M'gann put inside one of the DEO's cells instead of killing her. M'gann says that his blood is transforming him into a White Martian and there's no way to stop it. Sure enough, J'onn transforms his hand and sees that it's a White Martian. 

That night, Alex, Jimmy, and Winn arrive at Kara's apartment with comfort food. It quickly becomes obvious to Jimmy and Winn that Mon-El is into Kara. Maggie shows up to tell Alex that she's really important to her, so Alex agrees to play pool with him the next day.

The episode ends with Cyborg Superman using Supergirl's blood to infiltrate the Fortress of Solitude to find out about something called "Project Medusa".