What's Worth Watching: The 100 on The CW, Portlandia on IFC and more for Thursday, January 21

Matt Roush
The 100, Eliza Taylor
Cate Cameron/The CW

The 100 (9/8c, The CW): The toughest and strangest of all Young Adult TV adventures is back for a third grueling season of conflict on a post-apocalyptic Earth gone tribal. (Although in one sign of what some might construe as hope, Shawn Mendes entertains the troops at the piano during a brief pause in the action.) Most of the early action focuses on Clarke (Eliza Taylor), still in exile months after the explosive events on Mount Weather. She's being hunted by friends and foes alike, the latter referring to her as "Wanheda," which translates to "the Commander of Death." Sounds about right. This part of the show is riveting. Not sure what to make about Jaha's (Isaiah Washington) woozy head-trip in the surreal "City of Light."

Portlandia (10/9c, IFC): The blissfully silly alt-world populated by multiple incarnations of Fred Armisen and Carrie Brownstein takes flight—with drones—as the sixth season commences at the annual Pickathon music festival. Brendan and Michelle (Armisen and Brownstein), unwilling to fight the crowds and the heat of the outdoors, decide to give "virtual participation" a try, wearing goofy oversized helmets that give them a drone's-eye-view of the proceedings. Which, naturally, goes awry, and not just because of the confusion caused by dueling Flaming Lips bands.

Dark Net (11/10c, Showtime): A more sinister side of our dependence on tech can be found in this new docu-series, which exploits the more sordid and unusual backwaters of what's known as the "deep web." (Think: real-life CSI Cyber without the boring cops.) The first episode introduces us to a long-distance relationship defined by "digital domination," in which a woman from Tacoma gives her submissive mate in Tusla humiliating commands via "pervertible" smart phone. There's also a vignette about a victim of revenge porn and glimpses of a Tokyo lad who has fallen for an online avator. It's all enough to make you want to log out for good.

London Spy (10/9c, BBC America): You've never seen a spy story quite like this brooding five-part series by Tom Rob Smith (Child 44), starring the terrific Ben Whishaw (Spectre) as a young man whose romance with a mysterious, aloof stranger (Edward Holcroft) propels him into a surreal and harrowing mystery of identity, sexual and otherwise.

Inside Thursday TV: Fox's American Idol (8/7c), wraps its final round of auditions. What are the odds they've discovered one last superstar? … Christy (Anna Faris) has a rich new beau (Harry Hamlin) on CBS's Mom (9/8c), but the complication is that he's the dad of her ex's new wife (Sara Rue), whose discontent just makes Christy and Bonnie (Allison Janney) that much happier. … On Elementary (10/9c, CBS), Joan (Lucy Liu) is invited to dinner, alone, by Sherlock's cagey father, Morland (John Noble), piquing her curiosity and our suspicions as to his agenda. … Spike just renewed Lip Sync Battle for a third season, and with contests like this week's (10/9c), between black-ish co-stars Anthony Anderson and Trace Ellis Ross, we can see why.