When an investigation goes horribly wrong, Sherlock must testify in an official police inquiry which jeopardizes his and Watson’s future with the NYPD.

Sue Sylvester introduces the episode as a Christmas special that FOX did not allow to air from last year. The members of New Directions audition for roles in McKinley's living Nativity Scene. Meanwhile in New York, Rachel, Kurt and Santana work as Santa's elves at a mall.

April’s sisters arrive to help celebrate April’s upcoming nuptials and quickly get on her nerves. Matthew and Jackson are forced to work together when they witness a terrible accident, Callie and Arizona work hard to reestablish their relationship and Cristina is pressured to live stream an upcoming surgery. Meanwhile, a familiar face returns to the hospital.

Mary and Francis are forced to rely on one another when the castle is taken hostage, and Catherine shocks everyone when she makes a surprising proposal to try to save their lives. Meanwhile, Bash’s mother Diane tells Bash of her plan to have him legitimized.

As the team gets closer to the truth, loyalties are tested and relationships are pushed to the limit. Meanwhile, Cyrus has to deal with his own crisis and he realizes that he may have gone too far.

Sheldon faces a crisis after Leonard disproves his accidental scientific discovery. Meanwhile, Raj must stay with Howard & Bernadette for a week.

Stephen weighs flight against invisibility, Colorado legalizes pot, the GOP learns how to talk to women, and Alan Mulally discusses the Ford Mustang's 50-year legacy.

From "Smash", actress Anjelica Huston; Univision anchor Jackie Guerrido.

Stefan continues to offer Katherine his support while trying to mask his own pain, until Caroline shows up with an unusual form of therapy. After trying to make amends with Caroline, Elena grows so concerned about Damon that she turns to Aaron for help. Later, when Damon tells Elena about a terrible ordeal in his past that he has kept secret for decades, she shares the disturbing information she just learned about her own family. Finally, Aaron decides on a desperate course of action after a conversation with Dr. Wes.

While Neal delves further into the mystery of the Codex, Peter takes on a classified espionage case with a fellow FBI agent: his ex-girlfriend.