Sheldon has escaped to Texas, so the rest of the gang are left to decorate for Christmas on “The Big Bang Theory” (CBS at 8 p.m.), and with him gone, they start to think about what their lives would have been like had they never met Sheldon.

Dr. Wes unleashes a secret weapon to stop Damon from rescuing Elena on “The Vampire Diaries” (CW at 8), and that secret weapon makes Damon deal with a part of the past he thought was gone forever.

It’s April’s wedding day on “Grey’s Anatomy” (ABC at 9), but the rest of the hospital crew continues to clash. Meredith and Cristina attempt to settle things between them, Bailey tells Ben how she really feels, Shane puts himself into a perilous situation and Derek receives a life-changing phone call.

While in Washington, D.C., investigator Dave examines the link between a mailbox and a spy case on “Mysteries at the Museum” (Travel at 9) and how a pair of brass knuckles played a role in protecting a president.

Nostradamus shares a prophecy with Mary that leads her to make a big decision concerning Francis on “Reign” (CW at 9). Meanwhile, Clarissa finally pursues her goals and Kenna tells Catherine about Diane’s intentions with Bash.

The six remaining designers trek to QVC’s headquarters in Pennsylvania to fashion a red-carpet-ready gown on the latest “Project Runway All Stars” (Lifetime at 9). Mondo Guerra, Lisa Robertson and Elizabeth Moss serve as guest judges.

Now that the truth is out there, things will never be the same. After last week’s stunning conclusion, “Scandal” (ABC at 10) is back with all the individuals who were involved in the case experiencing their own repercussions.

There’s a slew of new connections and conflicts on “Parenthood” (NBC at 10), starting with Drew asking Crosby for girl advice. Then, Amber confronts Ryan about the amount of time he’s spending with his band and Julia and Joel unite for their family.

Actress Julia Roberts stops by the “Late Show With David Letterman” (CBS at 11:35), with musical guest Glen Hansard.

Comedian Kevin Hart and model Brooklyn Decker come to “The Tonight Show With Jay Leno” (NBC at 11:35), with a musical performance from Chris Young.

Actors Carey Mulligan and Scott Foley are on “Jimmy Kimmel Live” (ABC at 11:35), with musical guest Jeff Campbell.

Rachel Lubitz