- For the episode, see "".
- "What's the harm in letting me help?"
- "The harm is that you could get hurt. I'm not just talking physically. This has cost me friends, family. It's an obsession that has taken up two years of my life. And I don't want that to happen to you."
- —Kara Danvers to William Dey on the dangers of investigating Andrea Rojas.
"Dangerous Liaisons" is the fifth episode of the fifth season of , and the ninety-second episode overall. It aired on November 3, 2019.
On the eve of the worldwide launch of Andrea Rojas's VR contact lenses, Kara and William team up on an investigation that exposes a terrorist plot. Kelly and Alex celebrate an anniversary, but Alex's safety is in jeopardy.
Andrea is getting ready to launch her Obsidian North's "Collective Dream" VR lenses this coming Friday, in approximately 3 days. After a quick meeting with her staff, she dismisses everyone, while Nia tells Kara how disappointed she is, that Kara was unable to find a connection between Andrea and William who was once again sucking up to the boss. Kara awkwardly dismisses her, fully knowing, that William has been tracking their boss for years. She simultaneously texts William to meet her for coffee across the street, but on her way down runs into Kelly. Kara quickly suggests she get Alex a schadel XG-1000 motorcycle helmet for their date-aversary before rushing to meet William. While at the coffee bar she convinces him to let her help, while adding if he does, he will have access to the government base her sister works at. He reluctantly agrees, and they are both allowed temporary passes on the DEO premise. Alex allows them in for her interrogation of Breathtaker, but William loses his cool and Alex kicks him out. Outside he confesses he has lost friends to the cause.
After a facility in New Mexico is broken into Supergirl is called to the DEO, Supergirl has a quick briefing with Alex and Brainiac. Brainiac decides to allow his body to be taken over by the Aurafacian alien, they agree on a start and end phrase, but during the interrogation, Supergirl becomes upset at how little the Aurafacian alien cares for human life. Alex meets her outside and reminds her that was not Brainiac. Kara takes it upon herself to break into her boss’ office to look for clues but is almost immediately stopped when William arrives to do the exact same thing. William is unable to crack her computer, that Kara is able to find a secret hidden box. Inside is a photo of Andrea and Russell Rogers along with some jewelry and some other objects. Will admits the reason he has been so obsessed with uncovering the Rojas Family, is because two years ago his best friend was dating Andrea. The day before they met, his house was broken into and he never saw Russell Rogers again. Kira tried to console him, but is called away by Alex to New Mexico. After a brief physical confrontation with Rip Roar he stopped her with a Fusion Cannon. Supergirl radios J'onn and he flies her back to the DEO under solar lamps.
Lena and Hope are working together to try and convince Malefic to work with them. Once he awakens they give him three obstacles to overcome, trying to manipulate his brain waves in order to turn the would-be vicious creatures, harmless. After some persuasion, he agrees, provided Lena agrees to help him take out his brother. By the end of the day, Malefic has completed his tasks and turned the Maladorian Dendroasp completely harmless. However, when Lena declines to kill anyone for him he threatens to become violent, however, she stops him by using his Q-Waves against him. Telling Malefic he rather enjoys his place here with her, and he again becomes decile.
Meanwhile, Kelly has been planning her day around her and Alex's date-aversary, and leaves her a voicemail to meet her at the peer, reminding her she must be present for Andrea's big launch. Only to be attacked soon after.
Once Supergirl is feeling better, Supergirl is determined to stop whatever it is coming their way. Unfortunately, they are greeted with more bad news, as Brainiac explains the geyser is pumping out three cubic miles of water every second. At that rate, every coastal city in the world will start flooding in 12 minutes. The loss of life could be in the billions. Supergirl and J'onn immediately go to Lake Vostok in Antarctica where they fight Rip Roar and are finally able to beat him together. After they must seal the geyser and agree to fly around it together in perfect sync before Supergirl is able to freeze it with her breath. Successful they both head back to the DEO. Supergirl and Alex have a heart to heart before Brainiac interrupts them with bad news. Kara goes to William's apartment to give him the unfortunate news. Rip Roar is actually his missing friend Russell Rogers and it would appear that the Rojas Family is completely innocent, as the disaster would have lost them billions.
After a successful launch of her "Collective Dream" VR lenses Andrea gets into her limo only to be greeted by a member of THE shadow organization, known as Leviathan.
- Lex Luthor and Caroline O'Connor were both mentioned, but do not appear.
- The title shares the same name as another Season 5 episode from which in-turn was named after the novel Les Liaisons Dangereuses.
- This is one of a handful of episodes to explicitly indicate that National City is located on the Pacific Coast.
- Kelly & Alex both got a Schadel XG-1000 motorcycle helmet in matte black for their date-aversary.
- Kelly gave Alex one because she asked Kara what she should get Alex; Alex got one for Kelly so they could go riding together (she knew what Kelly was getting her because Kara told her).
- Kara forgot her coffee at the coffee shop when talking with William.
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