2014 Fall Finale prebiyu | TVLine 

Why You Need to Watch: Because you\'re in for a "bittersweet" holiday featuring "cute little flashbacks to Christmases of the past [with] the girls all together," teases executive producer Julie Plec. (Sadly, Bonnie is forced to celebrate alone in her "prison world.") And here\'s more scoop to stuff in your stocking: There are "some big, big,

big chapter-ending moves at the end of the episode that change a lot for everyone."

Why You Need to Watch: Oh, only because it is "arguably the most epic episode we\'ve ever done," showrunner Marc Guggenheim effuses. "It literally is a game changer in the sense that the series will never be the same afterwards. Everyone here, including the cast and the crew, we all feel like it is our strongest midseason finale yet."

Why You Need to Watch: It\'s the show\'s 200th episode, and it\'s going to be one trippy hour. First off in the \'50s-set homage to Alfred Hitchcock\'s films, Brennan is an LAPD detective and Booth is a… jewel thief? "We\'re examining the beginnings of Booth and Brennan in another situation," explains exec producer Stephen Brennan of the bizzaro hour. "Their jobs might be different, but their characters are the same to a large extent."

Why You Need to Watch: Against the backdrop of Christmas, Esposito and Lanie reach a defining moment in their relationship, while an episode-ending twist promises to "change the shape of the show" for at least a short while, Stana Katic tells TVLine. (And no, the actress says, it does

Why You Need to Watch: Two new arrivals make their debut: baby Boden and the Molly\'s II food truck! Meanwhile, paramedics Mills and Brett face a dangerous call.

Why You Need to Watch: Because someone might not make it out unscathed!  As the Intelligence unit stages a daring undercover robbery, a main character gets shotgun blasted. Elsewhere, Roman\'s old partner -- the woman he fell in love with -- rides along with him and Burgess.

Why You Need to Watch: Quickly, Grant Gustin, dish!!! "It\'s a huge turning point for the show and for Barry and what he knows," the star teases. "I can\'t say too much else about it, because I would definitely give something away." EP Greg Berlanti meanwhile promises a "taste" of the Firestorm character that will loom larger in the second half.

Why You Need to Watch: Simply put, the episode\'s title -- "The Trial" -- puts embattled Cary Agos\' freedom in the balance, and has him considering a plea bargain. Meanwhile, a joke between mother and daughter lands Alicia in political hot water. Bracing for a stern look from Eli Gold in 5, 4, 3, 2...

Why You Need to Watch: While Selina leads a new friend (Bruce, we shall assume?) on a perilous journey through Gotham to evade the assassins who are on her trail, Gordon is reassigned to duty at Arkham Asylum.

Why You Need to Watch: When Dr. Herman begins exhibiting some bizarre behavior, Arizona goes behind her back to get more information on her diagnosis. Meanwhile, Derek and Meredith\'s marital discord intensifies in the wake of a work-related disagreement.

Why You Need to Watch: "Chupacabra," the supernatural drama\'s midseason capper, "is a great episode," star Silas Weir Mitchell says. "The director is great. The filming is great. Things worked out."

Why You Need to Watch: Craving resolution to the questions of who killed Sam Keating — and why? "At this point, everyone has a theory on who did it," adds Katie Findlay, who plays drug dealer Rebecca. "So, I don\'t think it would be possible for the guilty party to be a

everything goes down, that\'s another story. We were all gasping at the table read."

Why You Need to Watch: "There\'s a major cliffhanger that leaves the entire family, Jane and Xo, in an emotional rollercoaster situation," teases Andrea Navedo.

Why You Need to Watch: "S.H.I.E.L.D. and HYDRA converge on the alien city they\'ve been racing towards, in a desperate fight to gain control of the obelisk," showrunners Jed Whedon and Maurissa Tancharoen tell TVLine.  "In the end, our team -- and our show -- will be changed forever."

Why You Need to Watch: Because whether or not they actually make it down the aisle, Rayna and Luke are gearing up for their big day, y\'all!

Why You Need to Watch: Because it\'s an "entire episode about Gibbs\' Rules," previews showrunner Gary Glasberg. "The rules have become a big part of the show\'s moral and professional compass, and who better than Tim McGee to guide us through the list."

Why You Need to Watch: Because Callen may be forced to reveal his true identity to girlfriend Joelle — who\'s been innocently caught up in a major software theft — in order to save her life. \'Tis the season!

Why You Need to Watch: The "very touching episode" connects the New Orleans crew with a deceased Navy Petty Officer in Afghanistan, previews exec producer Gary Glasberg, adding, "As Pride and Lasalle head to the Middle East for answers, Lasalle also obtains information on the whereabouts of his missing younger brother, leading to an emotional holiday for the whole team."

Why You Need to Watch: With the Frozen arc coming to a close, "Two of the show\'s most beloved relationships will be tested and changed forever as Storybrooke says goodbye to some of their own," series creators Adam Horowitz and Eddy Kitsis preview. "In the Enchanted Forest, things gets classically evil as we face off against an embarrassment of witches."

Why You Need to Watch: The conclusion of Rebekah\'s two-part visit to the Big Easy finds the Mikaelson siblings -- three of them, anyway -- coming together like never before. Joseph Morgan promises "great moments of levity" (finally!) as well as some "heartwarming stuff" for fans of TV\'s most dysfunctional family.

Why You Need to Watch: Because Mark Cyr (Jason Ritter) makes a surprise return -- and you just

he\'ll throw a wrench in the Sarah/Hank relationship. (Plus, judging by this exclusive photo, Joel and Julia are trying to make it work!)

Why You Need to Watch: Because not only does Mama Pope return, but Olivia makes a bold decision about how to deal with taking down Papa Pope. (Might that bold decision be related to this new promo that has Liv demanding to take "the kill shot”?)

Airdate: Two-parter airing Monday, Nov. 24 and Dec. 1 (Fox, 9/8c)

Why You Need to Watch: It\'s not an exaggeration to say that everything, from the series\' first moment on, has been leading to this episode. And with a tease like this from star Nicole Beharie -- "This is what we\'ve been waiting for. I hope everyone\'s ready. Lace up your bootstraps." --why

Why You Need to Watch: Dean finally makes a decision about the troublesome Mark of Cain plaguing him. Elsewhere, the daughter of Castiel\'s vessel, Jimmy, convinces the angel to break her out of a group home -- and then she ditches Cas (how rude!), leaving the Winchesters to search for her. As for Crowley, the King of Hell will face his biggest challenge yet.

Why You Need to Watch: Because you\'re in for a "bittersweet" holiday featuring "cute little flashbacks to Christmases of the past [with] the girls all together," teases executive producer Julie Plec. (Sadly, Bonnie is forced to celebrate alone in her "prison world.") And here\'s more scoop to stuff in your stocking: There are "some big, big, big chapter-ending moves at the end of the episode that change a lot for everyone."