Monday on TV

How I Met Your Mother (7 p.m., Ch. 2): Marshall and Lily forget that they were supposed to get Ted a date for Valentine's Day.

Chuck (7 p.m., Ch. 5): Chuck and Hannah get pulled into Agent Shaw's latest mission.

House (7 p.m., Ch. 13): It's a day in the life of Dr. Cuddy.

Accidentally on Purpose (7:30 p.m., Ch. 2): Billie accompanies Zack to his high school reunion.

Two and a Half Men (8 p.m., Ch. 2): Charlie can't control his jealousy.

Heroes (8 p.m., Ch. 5): Noah's life hangs in the balance as the good guys try to stop Samuel from killing thousands. This is the fourth-season finale, and it just might turn out to be the series finale, too, because the ratings have been bad. If it is the end, well, there's not much left to mourn. After a great first season, the show has done little but disappoint.

24 (8 p.m., Ch. 13): The international delegates convene in New York.

Life Unexpected (8 p.m., Ch. 30): Lux gets suspended from school.

Big Bang Theory (8:31 p.m., Ch. 2): Leonard can only choose one person to accompany him to visit the Large Hadron Collider on Valentine's Day.

CSI: Miami (9 p.m., Ch. 2): The team investigates a murder in outer space.

Castle (9 p.m., Ch. 4): A former major league baseball player is murdered.

Blueprint America: Beyond the Motor City (9 p.m., Ch. 7): A look at how America's transportation infrastructure has evolved and where it's going.

Secret Life of the American Teenager (9 p.m., ABC Family): Both Amy and Anne try to sort out their love lives.

Greek (11 p.m., ABC Family): Tensions boil over during a softball tournament.

Damages (11 p.m., FX): Ellen learns a dark family secret.