Chaos ensues as earthquakes ravage the city. James reveals himself as Guardian to a desperate mom. M'yrnn gives J'onn the first memory of their people. Imra and Brainy return to help.
M'yrnn sacrifices himself after saying goodbye to J'onn and the earthquakes stop.
Mon-El and Imra realize their marriage was never what it should be, and they part amicably.
Sam sees her mom in the valley. She wants to help her.
Brainy reveals that stopping Pestilence meant his distant relative lived and he has created a plague to wipe out A.I.'s. Brainy can no longer stay there. He tells Winn to replace him in the Legion. He tells him his shield design has saved countless lives in the future.
Winn discusses his potential move to the future with James. James tells him about unmasking, and how both decisions are hard.
Despite Kara's reluctance, they agree to kill Reign with Lena's Kryptonite if all else fails.
Sam wakes up and has powers.
Kara's team battles the Dark Kryptonians. Reign gets Kara in a choke hold, and Sam stabs her with a sword. Reign's laser eyes hit Alura and Mon-El, and she disappears in a pit of flames.
Kara takes Mon-El's ring to go back in time a few moments. She stops Sam from stabbing Reign. She uses the black rock to trap Reign in the valley.
Mon-El tells Kara that he has to go back to the future. He can't abandon the Legion, but he gives her his ring in case she ever needs him.
Lena tells Sam her blood tests reveal she is 100% human.
Winn tells James that he's decided to go to the future.
Alex tells J'onn she wants to quit to be a mom. J'onn tells her he wants her to take over as director of the DEO, meaning she won't have to be in the field as often. He leaves the DEO to follow in his father's footsteps.
James reveals to the world that he's Guardian.
Lena is running tests on the black rock.