1) “Unforgotten” season-opener, 10 p.m., PBS. Each year, this has a deep and demanding story. Now solemn cops — one divorced, the other fuming at her cheating husband and sister — tackle a tough one. There’s a widow, her daughter and a right-wing commentator (shown here), plus Afghan refugees, an Albanian loan shark and more. The result is compelling.
2) “The Princess Diaries” (2001), 8:33 p.m., ABC. It’s a fun night for ABC — an expanded “America’s Home Video” rerun at 7 and then this charming tale of an American teen who learns she’s royalty. There’s good work from Anne Hathaway, Julie Andrews and director Garry Marshall.
3) “Professor T” season-opener, 8 p.m., PBS. Last season ended with the death of Lisa, the likable deputy inspector. That shattered Dan (her police colleague and lover) and the already-troubled professor. This hour spends too little time on an iffy case, but adds fun with Rhian Blundell, as the new cop, and theater-great Zoe Wanamaker as the prof’s aunt.
4) “The Marlow Murder Club” season-opener, 9 p.m., PBS. British mysteries come in every shape — one six-week story on “Unforgotten,” six one-week ones on “Professor T” and three two-parters here. This first one is ingenious, wth a rich bridegroom seemingly dying alone.
5) ALSO: “Big Brother” (8 p.m., CBS) expands to two hours, pushing the “Tracker” rerun — a good one, with a retired cop searching for campers — to 10. Also, Fox has “The Quiz With Balls” at 7, followed by Gordon Ramsay reruns — “MasterChef” (a macaron mountain) and “Secret Service.”