Worth Watching: 'SVU' Hits 450, All-Star 'Big Bang,' 'Flack' on Pop, 'Desus & Mero' Late Night on Showtime

Matt Roush
Michael Yarish/CBS

A selective critical checklist of notable Thursday TV:

Law & Order: Special Victims Unit (10/9c, NBC): In a milestone few shows have achieved, SVU marks its 450th episode, just a few shy of the total number clocked by original mothership Law & Order — which ended in its 20th season, while SVU seems destined to be renewed for at least a 21st. Dean Winters returns for the occasion as Cassidy, whom Benson (Mariska Hargitay) enlists for help on a case in which a young man’s suicide leads to a child molestation investigation. William Sadler and Orange Is the New Black's Selenis Leyva are guest-stars.

'Law & Order: SVU' Season 20: All the Famous Guest Stars So Far (PHOTOS)

'Law & Order: SVU' Season 20: All the Famous Guest Stars So Far (PHOTOS)

This season includes an Emmy, Tony, and Golden Globe winner.

The Big Bang Theory (8/7c, CBS): When so many guest stars clamor to hop aboard a hit show on its final victory lap, it almost feels like an old-fashioned sweeps-month stunt. In a very funny episode, Star Trek icon William Shatner appears as himself, sending Sheldon (Jim Parsons) into a fanboy tizzy ("Will you call me Science Officer Cooper?" he begs) — and that's before he and the gang learn that the former Capt. Kirk is part of Wil Wheaton's weekly celebrity Dungeons & Dragons gathering. (Others on the eclectic invite list include True Blood/Magic Mike hunk Joe Manganiello, NBA legend Kareem Abdul-Jabbar and Kevin Smith.) The guys — and gals (see Magic Mike) — have their own reasons for wanting to crash the party, but only a lucky select few will be chosen.

Kaley Cuoco Shares Her Favorite 'Big Bang Theory' Episodes & Post-Finale Plans

Kaley Cuoco Shares Her Favorite 'Big Bang Theory' Episodes & Post-Finale Plans

Plus, the actress looks back on Penny's legacy and her mysterious last name.

Will & Grace (9:30/8:30c, NBC): More great guests: Alec Baldwin returns as Malcolm, turning to Grace (Debra Messing) to help him get back on Karen's (Megan Mullally) good side — if there is one. NCIS: LA's Barrett Foa plays Will's (Eric McCormack) flirtatious co-worker, and the great Andrea Martin appears as Zusanna, the sister of Jack's (Sean Hayes) former acting teacher and a new muse to reignite his love for performing.

Flack (10/9c, Pop): Stop me if you've heard the one about the ruthless anti-hero who's a wiz of a fixer when it comes to celebrities in deep crisis ("We call them challenges") but a mess in their own life. No, this isn't Ray Donovan, it's the story of Robyn (a brittle Anna Paquin), an American publicist (aka "flack") living in London who's up to her arched eyebrows in her clients' sordid sex scandals. "There are no good ones," she sighs in between taking hits of cocaine and bantering with the vicious vipers in her workplace. (Her boss is the terrific Sophie Okonedo, seriously slumming here.) Recommended mainly to those who don't already have enough unpleasantness in their lives.

Desus & Mero (11/10c, Showtime): The premium channel takes a plunge into the late-night space with the hip podcasters and TV personalities Desus Nice (Daniel Baker) and The Kid Mero (Joel Martinez), who'll riff on whatever's hot in the culture. Their first guest is the latest sensation to emerge from their home borough of the Bronx: progressive Congresswoman Alexandria Ocasio-Cortez.

Why 'A Million Little Things' Star James Roday Is a Scene Stealer

Why 'A Million Little Things' Star James Roday Is a Scene Stealer

He plays, Gary Mendez, a breast cancer survivor on the ABC drama series.

Inside Thursday TV: Emotions run high on ABC's A Million Little Things (9/8c) as Maggie (Allison Miller) undergoes surgery for her cancer, and her visiting mother (Melora Hardin) doesn't immediately warm up to Gary (James Roday)... For those missing NBC's Superstore, and can't wait for its return March 7, Paramount Network's Lip Sync Battle (9/8c) offers a sync-off between series stars Ben Feldman, who takes on Celine Dion's "It's All Coming Back to Me Now," and Lauren Ash, who channels Madonna's "Express Yourself"… A new mission on CBS All Access's Star Trek: Discovery (9:30/8:30c) puts Saru (Doug Jones) in the hot seat when a new signal appears over his home planet, raising new doubts about the Red Angel and its intentions… CBS's S.W.A.T. (10/9c) team tries to keep the peace at an LGBTQ pride festival after a hate crime riles the city. While Chris (Lina Esco) worries on behalf of her fellow LGBTQ citizens, the festival inspires Commander Hicks (Patrick St. Esprit) to reconnect with his estranged gay son (Sterling Beaumon).