TV icon Bob Newhart returns to his old stomping grounds - a CBS sitcom - when he appears on this week's episode of The Big Bang Theory (7 p.m., CBS/Ch. 2).
He guest stars as Professor Proton, the star of a kids' show that Sheldon (Jim Parsons) and Leonard (Johnny Galecki) loved when they were kids. And word is that Newhart may be back next season.
Elsewhere on TV ...
Community (7 p.m., NBC/Ch. 5): Abed is convinced that members of the study group were destined to meet.
American Idol (7 p.m., Fox/Ch. 13): Another contestant is eliminated.
The Vampire Diaries (7 p.m., CW/Ch. 30): Damon and Stefan try to turn Elana around.11
Two and a Half Men (7:30 p.m., CBS/Ch. 2): Alan attracts the attention of a married woman.
Person of Interest (8 p.m., CBS/Ch. 2): A virus causes the machine to malfunction.
Grey's Anatomy (8 p.m., ABC/Ch. 4): Bailey shuts everyone out.
The Office (7:30 p.m., NBC/Ch. 5): Jim comes back to Scranton to be with Pam; Andy tries to work up the courage to quit his job and pursue his dreams.
Parks and Recreation (8:30 p.m., NBC/Ch. 5): April receives life-changing news. (Season finale)
Glee (8 p.m., Fox/Ch. 13): Rachel gets ready for her call-back.
Beauty and the Beast (8 p.m., CW/Ch. 30): The mayor is shot.
Men at Work (8 and 10 p.m., TBS): Milo decides to break up with Molly.
Elementary (9 p.m., CBS/Ch. 2): Sherlock resumes his search for Moriarty
Scandal (9 p.m., ABC/Ch. 4): The team makes a shocking discovery about the mole.
Anger Management (10 and 10:30 p.m., FX): Charlie has one of his patients spy on Kate.