Jesse, Caroline and Stefan on "The Vampire Diaries." (Bob Mahoney/CW )

Sheldon makes a scientific breakthrough on “The Big Bang Theory” (CBS at 8 p.m.), but he feels it may haunt him for the rest of his career. After Howard makes a grand romantic gesture for Bernadette, Penny puts more effort into her relationship with Leonard.

Mysteries abound on this week’s “The Vampire Diaries” (CW at 8), with Matt trying to figure out what’s behind his blackouts and Jeremy’s newest startling confession. Elena and Damon attempt to help Stefan through a confusing time and Dr. Maxfield puts a plan in motion that threatens to change everything.

RETURNING SHOW: All your runway favorites are back and challenged with making fashion-forward punk looks for the season opener of “Project Runway All Stars” (Lifetime at 9). Debbie Harry is guest judge.

After critical acclaim this summer, CNN is airing “Blackfish” (9), a documentary about SeaWorld trainer Dawn Brancheau, who was killed in 2010 when the killer whale Tilikum grabbed her and yanked her underwater. Director Gabriela Cowperthwaite’s film raises a number of questions and also takes us through the 39-year history of orcas in captivity.

SERIES PREMIERE: Follow a group of traveling nurses assigned to work at an Orange County, Calif., hospital for 12 weeks on “Scrubbing In” (MTV at 10). Since relocating from across the country, they’ve left their hometowns behind for short-term contracts, with the added benefit of exploring an exciting new city.

SERIES PREMIERE: Rocco DiSpirito is coming to the aid of families whose restaurants are on the brink of failure on “Restaurant Divided” (Food Network at 10). The docu-series gives them a unique chance to reverse their fortunes.

Actors Robin Williams and Lizzy Caplan come to “The Late Show With David Letterman” (CBS at 11:35), along with musical guest Icona Pop.

Actress Emma Roberts joins animal trainer Dave Salmoni on “The Tonight Show With Jay Leno” (NBC at 11:35), along with musical guest Diane Birch.

Actress Lisa Kudrow and journalist Malcolm Gladwell come to “Jimmy Kimmel Live” (ABC at 11:35), with musical guest Kings of Leon.

SERIES PREMIERE: During the eight-episode season, late-night viewers will find out what happens behind the scenes when the “Workaholics” star is given a massive party budget and free rein at a Los Angeles mansion on “Adam Devine’s House Party” (Comedy Central at 12:30 a.m.). Naturally, things get a little crazy as some of Devine’s favorite comedians stop by to enjoy the party and perform stand-up sets.

— Rachel Lubitz