'Castle' sneak peek: Castle and Beckett's first Christmas

Rick Castle (Nathan Fillion) and Kate Beckett (Stana Katic) will be celebrating a very special Christmas this year on "Castle" -- their first as a bona fide couple.

They may not be roasting chestnuts and sipping eggnog, but they will be walking in a winter wonderland ... to find out who murdered Santa!

In "Secret Santa," the couple are called to a snowy crime scene in Central Park, to find a dead man matching the description of Saint Nick: white whiskers, red-and-white costume and stocking cap, black boots -- and Kris Kringle ID. Oh, and he seemingly fell from the sky.

Can the crimefighters solve the case and save Christmas? Find out when "Secret Santa" airs Monday, Dec. 3 at 10 p.m. on ABC.