Supergirl Season 4 Finale Recap With Spoilers: Lex Luthor's Evil Plan Revealed in "The Quest For Peace"

Last week, Supergirl faced something of a "worst nightmare" situation. Lex Luthor's manipulations had finally worked together to position the villain as a huge hero as he "saved" the United States from an attack by Kasnia and, then, "killed Supergirl" by appearing to take out Red Daughter. With Lex now in a position to be even more dangerous than ever before, it's up to the Girl of Steel and her allies to make one last push to expose him -- but is it too late?

Warning! Spoilers for tonight's Season 4 finale episode of Supergirl, "The Quest For Peace", below!

The episode starts 24 hours earlier with Red Daughter reporting back to Lex Luthor, apologizing for failing to kill Supergirl. He instructs her to go after Liza. Lex then puts aliens into some sort of battery-like chamber and uses their powers to power his Lexosuit. Jump to one hour before last week's ending. Lex and the President in the Oval Office with the president questioning Lex's certainty and the attack begins. Lex saves the United States and then meets Red Daugther on the beach, apparenlty killing her.

Supergirl tells Liza and Alex that she has to show the world the truth about Lex, but elsewhere, Lex has Red Daughter in one of the battery pods where he tells her how stupid she is for having ever trusted him. The president then names Lex new Director of Alien Affairs whlie an attempt is made on Ben Lockwood's life, but he's repowered himself with the Harun-El serum and survives. Elsewhere, Nia and J'onn have gone through the portal and ended up on Shelley Island -- where Lex has more of the batteries. At Lena's office, a still emotionless Brainy reveals what's going on with Nia and J'onn. Lena is summoned to the White House.

Lex reveals his plan to Lena and his mother: he's harnessing the powers of the aliens to use them as rechargable disposable batteries to power the world. He also plans to use the first batch of batteries to attack and destroy Argo and thus, Superman. Speaking of those batteries, J'onn and another alien create a distracton and fight their way to the control room and take the system offline restoring Nia's powers long enough for her to tell Brainy, Kara, and Alex about Shelley Island.

While Lex grandstands, Kara's expose publishes. At Shelly Island, Brainy figures out Lex's plan but Ben Lockwood shows up to fight Supergirl. A fight ensues while Brainy reaches Nia and J'onn but the launch cannot be stopped as the core is charged. However, J'onn decides to attempt to overload it no matter if it kills him in the process. When the sattelite doesn't fire, Lex suits up and departs for Shelly Island.

Supergirl ends up fighting Lex who is shocked she's alive. He came armed with Kryptonite. She came with her safety suit. At Shelly Island, J'onn isn't putting out enough power so Nia helps him and witnessing that is enough to restore Brainy's "humanity" who confesses his love for her. They manage to overload the core.

And now, a fight montage. Alex and James against Lockwood and Supergirl against Lex. James and Lockwood end up un-powering each other. The aliens in the batteries are released, including Red Daughter who arrives to save Supergirl just in time by taking a direct of blast of Kryptonite. She dies and Supergirl reabsorbs her -- as she had been created by the Harun-El at the end of last season. It superpowers Supergirl, who blasts Lex's Lexosuit, causing it to fail as he attempts to escape. Supergirl attempts to save him, but Lex claims he'd rather die and falls to Earth, his suit exploding with him in it.

Lena then finds him and depowers him and then shoots him. As he dies, he exposes Kara's secret to Lena. And now the wrap up: president is arrested, Supergirl restored, Alex enters a relationship with Kelly. Lena shows up at the gathering at J'onn's place as though nothing's wrong. Lockwood is in prison. His son becomes a spokesman for peace. Elsewhere, Eve tries to escape but is confronted and told Leviathian is watching. Elsewhere, The Monitor shows up with a Martian that's not J'onn and then pays Lex's corpse a visit.

Supergirl will return this fall on Sundays at 9 p.m. following Batwoman on The CW.

What did you think of tonight's season finale? Let us know your thoughts in the comments below.