Last week on Supergirl, Kara discovered that William isn't actually the terrible person and journalist she believed him to be. He's actually investigating their boss, Andrea Rojas. Now that Kara is aware of this, she's determined to help him get to the bottom of what Andrea is up to and that may mean following leads to dangerous places that even Supergirl may not be fully prepared for.
Spoilers for tonight's episode of Supergirl, "Dangerous Liaisons," below.
The episode opens with Andrea in an advertisement for Obsidian North's Collective Dream VR Lenses, promising that the lenses will make "imagination reality." She's ordering the CatCo staff to write about it in every single story until the launch goes live. Kara hides the truth about William for Nia, but texts him to meet her. She is offering William help from the DEO and wants to be involved, but William doesn't want Kara getting hurt. He grudgingly agrees to help.
At Lena's lab, she experiments on Malefic and puts him first into human form (he's Phil LaMarr!) and then tries to activate her tech. It backfires and he appears to incept Eve/Hope. At the DEO, Alex lets William observe the interrogation of the woman who tried to kill Elena Torres last week. She says that one of the people she's affiliated with is Rip Roar and William loses it. Turns out the guy killed William's best friend, but they never found his body. At Fort Summit Army base, Rip Roar is stealing something and attacks a guard, killing him.
While Kara is getting some advice from J'onn, Alex calls for her. Rip Roar stole Lex's Marathon Laser. Brainy suggests that they interrogate the spider-creature to see what they know about Rip Roar and what Andrea may be up to. Lena talks with Malefic who wants to know what's in it for him if he helps her. His deal is that he won't help her unless she disables the part of him that prevents him from killing J'onn and she agrees.
At the DEO, Brainy serves at the host for the spider creature -- the trigger word is a Keanu Reeves movie quote. Turns out the spider creature doesn't know anything, and it frustrates Supergirl to the point that she wants to confront Andrea. Alex talks her out of it. Elsewhere, Rip Roar meets with the older lady from the Season 4 finale. Rip Roar is working for Leviathan and she orders him to "change the world". Later, Kelly brings Alex dinner with Kelly so excited to share her major patient success story.
At CatCo, Kara and William break into Andrea's office looking for clues. He checks her computer, Kara scans the room and finds a secret panel with some interesting items and William reveals that his deceased friend, Russell, was involved with Andrea romantically and after talking about meeting her is when William discovered that Rip Roar had killed him. Kara is called away, suiting up as Supergirl to confront Rip Roar. He shoots her with a fusion canon, besting her. Later, as she recovers, she chats with J'onn who reveals that he doesn't think Russell is dead. The fusion canon also turns out to be a modification of Lex's Marathon laser.
The launch is about to happen, Malefic has a breakthrough at Lena's, Brainy discovers Rip Roar is headed to Antarctica. The plan appears to be to melt an ice cap and unleash a massive worldwide flood. Supergirl confronts Rip Roar and he ends up setting off a massive tidal wave poised to take out the entire West Coast. J'onn apprehends Rip Roar who claims he doesn't know who is behind things and now it's up to J'onn and Supergirl to stop the damage. Brainy says Dreamer needs to be on the case as well. Elsewhere, the VR lenses launch begins.
At CatCo, William confronts Andrea, but it turns out it is only in his VR world. As the wave approaches the coast, Dreamer tries to hold it back while people in their lenses are dazed and unaware. She manages to dissipate the wave as J'onn and Supergirl fix the geyser that started it all. The day is saved. At the DEO it turns out that Rip Roar's tech is biologically adhered to him and the evidence looks like Andrea wasn't behind the attack. Kelly struggles with having seen the wave nearly take out the city and Alex, too. Malefic believes that Lena has removed his ability to kill J'onn, but she actually double crossed him and instead developed tech that lets her incept him.
At William's, Kara reveals that Rip Roar is Russell. Elsewhere, Andrea gets into a limo and the Old Leviathan Lady is waiting for her and wants her to deal with Rip Roar.
Supergirl airs Sundays at 9/8c on The CW.