FINALE WATCH: “Happy Endings” (ABC at 8, 8:30) Status: unknown. In what may be a first, ABC launched its own “save this show” campaign, so this doesn’t bode well for the sitcom’s future as its wraps up Season 3 — particularly as the show has been shipped to Friday nights. Anyway, in the possible series finale, we finally meet Alex and Jane’s never-before-seen older sister, who is getting married.

Chef Ramsay heads to Music City on “Kitchen Nightmares” (Fox at 8) to help out a couple struggling to find a new customer base for their Cajun restaurant, as business hasn’t been the same since they moved from Mississippi to Nashville after Hurricane Katrina.

An ice cream business that originally didn’t impress the entrepreneurs gets another look on “Shark Tank” (ABC at 9), while a California truck driver has an idea for frozen gumbo.

It’s yet another “24” reunion on Kiefer Sutherland’s “Touch” (Fox at 9) when D.B. Sweeney — who played private security company contractor on the former Fox drama — guest-stars as an Aster Corps enforcer who has a run-in with Martin.

SERIES PREMIERE: New reality show “Maron” (IFC at 10) chronicles the daily life of comedian Marc Maron, host of a very successful podcast, and owner of several cats. In the first episode, Marc decides to get revenge on a mean Twitter user.

RETURNING SHOW: Syfy brings “Merlin” (at 10) back with a run of five new episodes, before the imported BBC series wraps up for good on May 31.

Katie Lowes of ABC’s “Scandal” joins the crew on “Fashion Police” (E! at 10) for the night, helping Joan Rivers critique outfits from the week.

Danny promises to protect someone on “Blue Bloods” (CBS at 10), and falls apart when he can’t live up to his word; meanwhile, the members of the Reagan family all suffer a loss due to a housing project gang.

RETURNING SHOW: Continuing its goal to feature comedians, “The Half Hour” (Comedy Central at midnight, 12:30) returns for Season 2 and spotlights stand-up sets every week, starting with Dan Soder and Nikki Glaser.

Actor Nathan Lane and comedian Joe Matarese visit “Late Show With David Letterman” (CBS at 11:35), along with country singer Kacey Musgraves.

“The Tonight Show With Jay Leno” (NBC at 11:35) hosts actor Chris Evans, director Kevin Smith and a performance by British band Various Cruelties.

— Emily Yahr