Reign crashes in on James and Lena looking for Ruby. Lena sprays her with Kryptonite. 

The Legion determines that it is time for them to return to their time. 

Lena tells Alex where Ruby is, and she goes there to protect her. She's in Lex's mansion.

Kara and J'onn go to see Sam's mother.She reveals that she knows Sam is Reign. She doesn't want to leave, so they agree to wait for Reign to arrive. 

Kara and J'onn set a trap for Reign, but they weren't expecting her to have Purity and Pestilence's powers. Her mom comes out and tries to get through to her, but Reign kills her. 

Brainy bugged the DEO, and learns that the odds of Supergirl defeating the new Reign goes up significantly if one Legion member stays behind. 

James tells Lena she needs to tell Supergirl she can make Kryptonite to help stop Reign. 

J'onn and Kara ask J'onn's father how he appealed to the White Martians to see if they can use his strategy against Reign.

Imra tells Mon-El he should go back and help Kara. 

Lena brings the Kryptonite to Supergirl, who is angry that she lied to her. 

Ruby sneaks out of the house and calls her mom. Reign hears and finds the house. Mon-El arrives back in time to help Kara since she can't use the Kryptonite and J'onn is still injured. 

Kara, Mon-El, and Alex fight Reign, but Kara uses her code against her and convinces her she can't kill an innocent girl. Mon-El hits her with the Kryptonite. 

Supergirl apologizes to Lena and tells that she does trust her. Lena plans to find a cure for Sam. 

Lena runs into Kara and tells her she can't trust Supergirl anymore.