Supergirl investigates a mysterious symbol popping up all over National City, tracing its origins back to an ancient prophecy and the mark of the World Killer, Reign. Meanwhile, the tension between Lena and Morgan Edge continues to build, causing James to step in and offer up some protection, and possibly igniting a spark in the process.
I Hear (Click, Click, Click) — The Rosebuds
Kara and Alex's Christmas party; Kara offers everyone the famed Danvers eggnog; James and Lena chat over drinks; J'onn insists Winn play a certain Christmas song for his father.
Jingle Bell Rock — Daryl Hall & John Oates
Winn changes the music; M'yrnn expresses admiration for hot chocolate; Winn realizes that M'yrnn doesn't know what Star Wars is; Alex & Kara ask each other how they're doing; Samantha and Ruby arrive.
Christmas Time — Sonny Ellis
Winn and Kara stop by the alien bar and run into Mon-El and Imra hangout; Winn pulls Imra away to grab a beer; Kara and Mon-El awkwardly attempt try having a friendly conversation with one another.
Gonna Be Christmas — The Weeklings
Ruby asks Alex about her interactions with Supergirl; Lena comments on how tired Samantha looks; Kara and Samantha tease Lena about her and James chemistry; J'onn tells Kara they need to leave.
Rockin' Around the Christmas Tree (Single) — Brenda Lee
Supergirl and Reign crash an building and into an office Christmas party, they begin to brawl until they break through the ceiling.