Everything old is old again in Richard Osman’s latest comic mystery, “We Solve Murders.”

It’s not part of Osman’s “The Thursday Murder Club” series, but his fifth book to feature detectives who are old enough to collect pensions and read Modern Maturity. And it’s part of a wave of mysteries with sleuths who are more likely to pore over clues while clicking away at their knitting than to race down an alley after a maniac.

Many current series feature older detectives, so it’s a legit trend. But it’s not exactly new.

These contemporary books, including beloved series by Jesse Q. Sutanto and Alexander McCall Smith, follow in the footsteps of the legendary Agatha Christie. Her Hercule Poirot (”And Then There Were None”) was already a retiree when he made his debut in the 1920s. And Miss Marple was described as quite elderly when she appeared in her first novel, “The Murder at the Vicarage,” in 1930. (Both continued to detect for more than four decades, barely aging in the process.)

New, older detectives are popping up all the time: Brothers Ian and Will Ferguson just released “Mystery in the Title,” which features a has-been TV actor who keeps stumbling over corpses. And next June a series debuts with a Jamaican-British woman who’s retired from nursing but not from solving crimes, “A Murder for Miss Hortense.”

Here are five series, in order of preference, with gumshoes who, like Miss Marple and “Murder She Wrote”'s Jessica Fletcher, are lifelong learners. Because these characters have so much character, the books often de-emphasize crime solving and pump-up humor and human interaction. So, we’ve included a ratio to help you determine how much mystery to expect:

The Great Hippopotamus Hotel

Alexander McCall Smith

Who’s detecting? Precious Ramotswe, a “traditionally built” Botswanan who operates the No. 1 Ladies Detective Agency, along with assistant Grace Makutsi. They’re self-taught detectives, so it’s a good thing this sweet, humane series finds them investigating not murders but why a daughter is suddenly ill-behaved or a small business’ ledger no longer balances. (Due Oct. 15.)

Ratio: 20% mystery/80% African life.

Why age is a plus: Precious has a ton of experience evaluating human nature, which has proved useful in the series’ 24 previous books, with a new one almost annually since “The No. Ladies Detective Agency” debuted in 1998. We’re not sure how old she is, but she already was middle-aged in 1998 and she seems to age roughly in real time. That means she has developed a broad network of distant relatives that reaches to the corners of her small African nation, so she almost always knows somebody who knows somebody who can help solve her latest case.

The Thursday Murder Club

Richard Osman

Who’s detecting? Like the “Mission: Impossible” gang, it’s a group of people, each with a specific skill set. Former special agent Elizabeth enlists three neighbors to help solve the murder of a property developer at the retirement village where they live: Elizabeth has detecting know-how developed over many decades; Joyce is a talker who sometimes elicits surprising information from suspects; Ibrahim is a silent type whose psychiatry background often comes in handy; and tough guy Ron, a former union activist, never trusts anyone or backs down from a challenge. “Thursday” appeared in 2020 and Osman produced a sequel in each of the next three years (”The Last Devil to Die” is the most recent). The next one is due in 2025.

Ratio: 70% murder/30% chess and tea.

Why age is a plus: Collectively more than 300 years old, the Thursday Murder Club members are underestimated by virtually everyone they meet — and they’re good at using that to their advantage.

We Solve Murders

Richard Osman

Who’s detecting? First the bad news: Osman’s latest is not a “Thursday” book. The good news? It’s almost as much fun, and it’s not all that different. Instead of the four “Thursday” retires, “We Solve Murders” has three sleuths: a randy, 80ish romance novelist who’s a bit like an American Joan Collins and two Brits, a retired police officer and his daughter-in-law, a security expert. All three get involved in a string of murders at which clues are planted to cast suspicion on the daughter-in-law.

Ratio: 50% mystery/50% comic character stuff.

Why age is a plus: The police officer has practice at fading into the background so he can observe, a quality that comes in handy, and the novelist has accrued a lifetime of cash, private planes and influential friends, all of which play a part in solving the murders.

Vera Wong’s Unsolicited Advice for Murderers

Jesse Q. Sutanto

Who’s detecting: Vera, who’s 60 and bored, is a widow. She has lots of time on her hands because business is slow and her adult son, rebelling against her meddling, ignores her. She operates a tea shop at the beginning of “ Advice for Murders,” but when it is trashed and a body is left behind, she shifts from brewing tea to hunting clues.

Ratio: 60% mystery/40% matchmaking.

Why age is a plus: Vera doesn’t know much about detecting (she often makes wildly inaccurate guesses), but she’s learned a lot about mixing teas to create exactly the blend a customer needs. That tea savvy turns out to be a metaphor for an uncanny insight into human behavior. Vera thinks she knows what’s best for everyone — and she might be right. A sequel, “Vera Wong’s Guide to Snooping (on a Dead Man),” is due in April 2025.

Agnes Sharp and the Trip of a Lifetime

Leonie Swann

Who’s detecting? Agnes, an 80ish British woman, gets help from a handful of elderly boarders, some of whom — like Agnes — have a police background. “Trip of the Lifetime” is the second in the series, following “The Sunset Years of Agnes Sharp.”

Ratio: 70% mystery/30% chit-chat.

Why age matters: One of the most compelling things about “Trip of a Lifetime” is that it explicitly pays homage to Miss Marple. Agnes gets an unexpected trip to a deluxe resort, where a victim is found clutching a copy of “A Caribbean Mystery,” a Christie book in which Marple is given a trip to a deluxe resort. That feels like both a hat tip to Christie and an acknowledgment that senior sleuths have a superpower: six (or more) decades of life experience. The “Agnes” books would be more satisfying if Swann told us more about her characters, especially the victims. It is compelling, though, how Agnes meets her fellow crime solvers: Strapped for cash, she must take in renters, who form a sort of sleuth commune. And that she has had trouble sleeping as she has aged, which gives her lots of time to hunt for clues.

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