SUNDAY: The absorbing British Masterpiece mystery series that explores the emotional consequences of long-unsolved murders returns for a sixth season. Detectives Sunny Khan (Sanjeev Bhaskar) and Jessica James (Sinéad Keenan) face a difficult challenge when human remains — a spine and a leg — are recovered from a marsh, the trail leading to a disparate array of suspects whose connections aren’t apparent as they’re slowly introduced in the first of six episodes. The lives about to be rocked by the cold-case squad’s investigation include a college professor (Victoria Hamilton), an Afghan immigrant (Elham Ehsas), a young man with autism (Maximilian Fairley) and an outspoken TV commentator (MyAnna Buring).

SUNDAY: Also from Masterpiece, and not to be confused with the upcoming Netflix movie The Thursday Murder Club (also based on a series of novels), this whimsical crime dramedy opens its second season with amateur sleuths Judith (Samantha Bond), Suzie (Jo Martin) and Becks (Cara Horgan) invited to an aristocrat’s garden party. The occasion: a celebration of the host’s latest engagement, though not everyone in his family seems thrilled. When the guest of honor is killed by a falling bookcase in a classic locked-room mystery, leaving behind a missing revised will, the snoops need to convince their policewoman friend Tanika Malik (Natalie Dew) that the death wasn’t an accident.

SUNDAY: Sunday’s British mystery bonanza opens with the fourth season of the cerebral whodunit set at Cambridge University, where criminologist professor Jaspan Tempest (Ben Miller) helps the police solve crimes. Joining the cast: veteran character actress Zoë Wanamaker as Jasper’s aunt Zelda, an old flame of the Dean (Douglas Reith).

SUNDAY: The time has come to “Fight” (the episode title) in the apocalyptic season finale of the thriller based on Stephen King’s bestseller (there will be a Season 2). The young telepaths imprisoned in the Institute, led by the gifted Avery (Viggo Hanvelt), turn on their captors, triggering what cadaverous security chief Stackhouse (Julian Richings) warns will be a “final solution.” From the outside, escapee Luke (Joe Freeman) and former cop Tim (Ben Barnes) return to the site to play hero. But the Institute’s lethal director Ms. Sigsby (Mary-Louise Parker) is known to play dirty, so will anyone emerge intact from the confrontation?

SUNDAY: Photographer Ami Vitale captures a desperate mission to rescue the endangered species of the northern white rhinoceros from extinction in a powerful nature documentary. With only two surviving females on the planet, scientists devise a plan for the first-ever surrogate rhino pregnancy, which may be the last and best chance to propagate the species.

INSIDE WEEKEND TV:

• Double Scoop (Saturday, 8/7c, Hallmark Channel): What could be more suitable as a late-summer treat than a romance framed around ice cream? Taylor Cole and Ryan McPartlin are ad execs and former colleagues vying to land a small-town dairy farm and ice-cream producer as a client. Down on the farm, their rivalry thaws. Make mine strawberry.
• Girl in the Cellar (Saturday, 8/7c, Lifetime): History repeats itself in a fact-based cautionary drama, starring Kyla Pratt (Call Me Kat) as Rebecca, an overprotective mother who confines her wayward daughter (Kelcey Mawema) to the same basement cellar where Rebecca was trapped as a child by her abusive father.
• American Pie (Saturday, 8/7c, TBS): Dinner and a Movie hosts Jason Biggs and wife Jenny Mollen welcome Biggs’ costars in the 1999 comedy — including Alyson Hannigan, Mena Survari, Chris Klein, and Shannon Elizabeth — to share memories during a special screening.
• U.S. Open (Sunday, noon/ET, ABC): Game play at the tennis Grand Slam tournament starts on Sunday for the first time at the USTA Billie Jean King National Tennis Center. Coverage moves to ESPN2 at 3 pm/ET.
• Naomi Osaka: The Second Set (Sunday, streaming on Tubi): A profile of the former U.S. Open champ, who’s expected to play in the first round, focuses on her return to the game after the birth of her daughter, Shai.
• New Orleans: Soul of a City (Sunday, 9/8c, CNN): A preview of a docuseries scheduled for October chronicles the “Rebirth of the Superdome,” marking 20 years after Hurricane Katrina forced citizens to take shelter at the arena as well as the 50^th anniversary of the iconic stadium. Followed by a timely installment of The Whole Story With Anderson Cooper (10/9c), with national correspondent Nick Watt exploring the growing phenomenon of legalized sports betting.
• The Yogurt Shop Murders (Sunday, 10/9c, HBO): The true-crime docuseries ends with questions still lingering about the murders of four teenage girls in Austin in 1991. When the two main suspects were released on bond with charges dropped in 2009, the men continue to live under a cloud of suspicion while detectives keep looking for answers.