TV tonight: 'Riverdale' mixes Christmas and danger in fall finale

Riverdale
CW, 8 ET/PT

The Riverdale kids' crusade against the Black Hood gets riskier in the fall finale, darkly titled "Silent Night, Deadly Night." Betty (Lili Reinhart) and Archie (KJ Apa) have been trying to take down the murderer all season, and their mission leads to a dangerous showdown. Veronica (Camila Mendes) has to confront the demons in her family when she uncovers a huge secret Hiram (Mark Consuelos) has been hiding. But there's still room for some Christmas spirit, especially from Cheryl (Madelaine Petsch), who is determined to celebrate despite her mother's warning that they can't afford their usual extravagant affair. 

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Modern Family
ABC, 9 ET/PT

It's a big week for fall finales, and Modern Family is also calling it for 2017. Claire (Julie Bowen) scores a big opportunity for Pritchett's Closets and wants some recognition for her work. Pam's (Dana Powell) ex-boyfriend Bo (guest star James Van Der Beek) shows up, giving Mitchell (Jesse Tyler Ferguson) an excuse to get his sister-in-law out of the house. 

The Librarians
TNT, 8 ET/PT

The lighthearted adventure series premieres its fourth season, and it's starting off with a dangerous and exciting new mission. A secret sect of the Vatican discovers an ancient map that shows the locations of the four cornerstones of the very first Library, Flynn (Noah Wyle) and the Librarians set out to stop them from destroying it.