Mxyzptlk asks Kara to marry him. She tells him she's flattered, but no. He takes it as a challenge to make her fall in love with him. 

Kara tells Mon-El she wants to celebrate Valentine's Day with him once they get rid of Mxyzptlk. 

Maggie tells Alex she hates Valentine's Day. 

Winn meets an alien girl at the bar. She saves his life and then asks him to dinner. 

Mon-El wants to kill Mxyzptlk, but Kara says they don't kill. 

Alex confesses to Kara that she's disappointed that Maggie doesn't like Valentine's Day. 

Parasite attacks and Kara and Mon-El fight it. Mxyzptlk joins in dressed as Superman to help. He's creating havoc so he can play the hero. Mon-El says the way to send him back is to get him to say his name backwards. 

Alex tries to do something romantic for Maggie, and she gets angry. She tells Alex that her coming out was actually terrible. She told a girl she likes her on Valentine's Day and it went badly. 

Mon-El challenges Mxyzptlk to a duel for Kara's heart. Kara arrives as Mxyzptlk is about to kill Mon-El. She tells him she'll marry him. She tells him to meet her at the Fortress of Solitude. 

Kara sets the Fortress to self destruct. She tells him she'd rather die in there than be with him. He begs her not to kill herself. She tricks him into writing his name backwards to stop it and he's sent away. 

Winn and Lyra have dinner and decide to take things slow. 

Maggie surprises Alex with a belated Valentine's Day prom. 

Mon-El apologizes to Kara for his behavior, and the two finally kiss.