Supergirl Recap With Spoilers: Lena's Plan Revealed in "Tremors"

Last week on Supergirl, Leviathan's role as the looming threat over the series' fifth season became a little sharper. Not only did we get the origin for Acrata through a series of flashbacks revealing the demise of the friendship between Andrea Rojas (Julie Gonzalo) and Lena Luthor (Katie McGrath) but we also saw Lena translate the Medallion of Acrata to discover the term "Leviathan". This week things go to the next level with Leviathan becoming more of a tangible threat, but, more than that, Supergirl will finally discover the truth about her so-called best friend, a discovery that could change everything going forward.

Spoiler's for tonight's episode of Supergirl, "Tremors," below.

The episode opens with J'onn and Supergirl sparring to prepare for Leviathan, though they have no idea who or what Leviathan is or when they will strike. Supergirl has a bad feeling about everything. J'onn suddenly collapses. At Lena's, the older Leviathan Lady demands the Medallion from Lena and she refuses. Lena tells Hope that she wants to go find the weapons held at the Fortress so she can use one of them for her big plans -- and doesn't fear Leviathan as Supergirl will save her.

J'onn reveals he's been having visions of Malefic. Elsewhere, the Leviathan Lady chats with Rama Kahn -- Leviathan Lady's name is revealed to be Margot -- they're not thrilled about the Medallion situation. A mystery woman offers her assistance with his aim to take care of the planet. He refuses. At the L Corps gathering, Rama Kahn shows up to collect the Medallion and Lena calls on Supergirl for help telling her it was Leviathan.

At the DEO, Brainy gives them a little history lesson referring to the Leviathan guy - Rama Khan -- as being very old alien who has been around for countless major events with unknown powers. Lena suggests that Lex would know how to deal with this and Supergirl reveals that yes, some of Lex's worst weapons are at the Fortress and Supergirl suggests Lena comes with her.

J'onn meditates and tries to figure out what is going on with him by reaching out to his father's spirit. His father reveals that Malefic is, in fact, physically nearby and is across town, not the Phantom Zone. Brainy continues to investigate Rama Khan's attack and in doing so, locates Rip Roar who has been turned into a bomb of some sort, exploding and hurting Alex and Brainy in the process, though Brainy can fix himself while Alex collapses.

At the Fortress, Supergirl has to quickly disable safety protocols to protect against Luthors while back in National City, J'onn discovers that Malefic is currently a prisoner but J'onn will have to make a choice between banishing his brother or saving his soul. At the DEO, Kelly sidelines Alex, who has a concussion. At the Fortress, Lena uncomfortably recalls the Kasnia incident as she continues to play Lena. Elsewhere, Rama Khan is frustrated that he can't find Lena and the Medallion, but he figures out they are in the Fortress.

In the Fortress, Supergirl gets information about Rama Khan, revealing he's from a sister planet to Krypton while Lena uses the quantum processor to send a message to Brainy -- except she's really using it for other purposes. They eventually get to the weapons, including Myriad which is pretty much the item Lena needs. They settle on a sonic cannon to use against Rama Khan, though. Meanwhile, Brainy is having some aftereffects of the blast and puts together that Leviathan's headquarters are in National City. He rushes up to tell Alex, just as Kelly breaks up with her.

Alex and Brainy investigate the presumed location of Leviathan's headquarters and infiltrate. Alex calls for Supergirl, but Rama Khan shows up at the Fortress so they fight, with Supergirl realizing that while Rama Khan can bend the earth, the Fortress isn't Earth -- it's technically Krypton. Lena shows up and hits him with the modified gun, but Rama Khan escapes. Lena disappears and Supergirl then busts her stealing Myriad and Lena confesses.

She tells Supergirl that she killed her brother and that Lex exposed her identity, pouring her heart and her pain out at Supergirl and it's revealed that Lena set up the Fortress to turn against Supergirl and let her escape with Myriad. In National City, J'onn discovers his brother at Lena's lab and say she won't send him back to the Phantom Zone. He begs for Malefic's forgiveness and offers his mind for his brother to see his truth. It works. Malefic sees and understands. The brothers embrace. Alex visits Kelly and says she wants to help her the way Kelly helped her, their relationship is saved, and they also embrace. In the Fortress, a heartbroken Kara remains alone, trapped.