A new project can always use a helping hand — some popular IP, a respected brand name — to skip to the front of the line and cross the velvet rope to an audience. This week sees two new mystery series with literary roots, which is not necessarily to say in literature. "Neagley," now streaming from Prime Video, spins off from "Reacher," born in the novels of Lee Child. "Agatha Christie's Tommy & Tuppence" on BritBox is "based on the stories and characters of Agatha Christie," which the detectives among you have deduced has something to do with … Agatha Christie.

At the same time, such offspring have something to live up to, expectations to meet, a bar to clear that's set a little higher than if they were completely original. (Or as original as any mystery can be after a million have been written.)

Tommy and Tuppence, a pair of eventually married investigators, first appeared in Christie's second novel, "The Secret Adversary," continued in a series of short stories collected in 1929 as "Partners in Crime," and made return visits in the novels "N or M?" (1941), "By the Pricking of My Thumbs" (1968) and "Postern of Fate (1973), her final book, though not the last to be published. The characters have come to television twice before, in the the delightful 1983 "Partners in Crime: Tommy and Tuppence," set in the 1920s, which faithfully adapts several of the short stories, and a 2015 series, also titled "Partners in Crime" and based on "The Secret Adversary" and "N or M?," which has a Cold War background and an espionage theme. (Both those series are available to stream, on BritBox and Acorn TV, respectively.)

The new series, which stars Antonia Thomas ("The Good Doctor") as Tuppence and Josh Dylan ("The Buccaneers") as Tommy, is set in the present day, reupholstered for contemporary tastes without going overboard in terms of style and sexiness. (The characters are nearly 100 years old, and their personalities are transferable, so why not?) Written by Phoebe Eclair-Powell, it comprises three stories over six episodes, with a longer mystery running below and the halting romantic do-si-do sprinkled on top. The first story, involving a murder at a costume party, takes its cues from the short story "Finessing the King"; the third is a version of the missing children cold-case in "By the Pricking of My Thumb." I could locate no source for the middle mystery, but its theatrical setting is a favorite of such series; any that last long enough will eventually tread those boards.

The list of crime-solving couples on page and screen is long, but Tommy and Tuppence are arguably the first, preceding Nick and Nora Charles by more than a decade. Although Tommy gets top billing, Tuppence, as the more impulsive, less conservative partner, focuses your attention (and his), and this is as true of Thomas as it was of Francesca Annis, in the first adaptation, and Jessica Raines, the best reason to watch the 2015 series.

In this telling, Tommy has been made a successful crime writer, who is having trouble with his next book; Tuppence is a struggling actress, back visiting from America. (There's a husband there, to complicate things.) They meet, or re-meet, cute — they dated long ago — literally bumping into one another, in time-honored fashion, at a wedding where the guests are dressed as Alice in Wonderland characters; he's a friend of the groom, and she's filling in as a cater waiter. Then comes murder.

Imelda Staunton plays Tommy's Aunt Ada, a retired private eye living in a posh retirement home, who will offer occasional gnomic guidance a la, "You can't pickle a pig and darn your stockings at the same time." That we see her writing in a journal, and that she narrates the series, makes her seem like a Christie stand-in, or an echo of Jane Marple, but, given her surroundings and former profession, she presents more as Elizabeth Best in Richard Osman's "Thursday Murder Club."

Where the earlier series are essentially light-hearted, murder notwithstanding, the new "Tommy & Tuppence" is more romantic drama than comedy. It rolls rather than rollicks. There will be occasional flurries of action and tense situations, but it's a leisurely watch — though not slow, in the pejorative sense. It's well produced and very nicely shot, with plenty of admiring close-ups of the attractive stars. That it might turn silly or obvious from time to time is not really a problem or unusual in these sorts of things.

Things do heat up at times in "Tommy & Tuppence," but they stay mostly hot in "Neagley," with Maria Sten taking her recurring "Reacher" role to center stage. "Reacher" star Alan Ritchson is on hand in the early minutes to launch his sidekick on her new show, helping her nail some kidnappers and taking in a Cubs game at Wrigley Field to sell the series being set in Chicago and not just, um, Toronto. Neagley — the name of a brainy nerd in a frat comedy more than an action star, but nothing to be done about that — brings into the new series her pathological dislike of being touched, which does not get in the way of her punching, and her love of cold cereal. But where she was something of a ray of sunshine in "Reacher," she has been loaded here with issues, including a dying father who isn't telling her something. "I don't have trauma," she insists, but we know better. She's grim, and sometimes a bit of a jerk.

Created by Nick Santora, who also created "Reacher," and Nicholas Wootton, who has written for scads of crime shows, "Neagley" builds its world from scratch, where the parent show has had the benefit of being built upon books.

It starts out pretty well as a shoe-leather detective show, as Neagley investigates the death of an old friend who walked naked into the path of an elevated train. (It's personal.) As one thing leads to another, a team will assemble around her: honest Det. Hudson Riley (Greyston Holt), descended from three generations of smugglers, with things to prove; Renee Birdwhistle (Adeline Rudolph), an office colleague who wants to be a P.I.; and Keno (Jasper Jones), a petty, larcenous street kid with a good heart. Call them Fred, Velma and Shaggy.

What comes after is often preposterous and teeming with cliches — the sort of things you might have encountered in a second-tier series back in the 1980s — and craziness. There are corporate villains, psychedelic drugs, mad scientists, crooked cops, yet another male-female team of hit people, Old Testament stoning and a chair that converts into a coffin. (Blofeld would have loved it.) Damon Herriman plays a cult leader in the image of David Koresh, complete with aviator glasses and rock star dreams. (He'll perform a bad rendition of Iggy Pop's "The Passenger" and quotes Depeche Mode — "I am your own personal Jesus" — when he harangues his fannish flock.) It seems not impossible that Herriman's having twice played Charles Manson (on "Mindhunter" and in "Once Upon a Time... in Hollywood") might have inspired his casting. As many a TV detective likes to say, there are no such thing as coincidences.

As in "Reacher" and every action film ever, events will lead to a battle royale whose outcome is predetermined by the nature of this show. Like Tennyson's Sir Galahad, our heroes have the strength of 10 because their hearts are pure — or, you know, pure enough — so any car chase or fight scene we watch as choreography rather than as a contest. (This is not necessarily a bad thing; there's enough tension in the world.) Though much of the action is muddled by a superfluity of angles and edits, Sten looks very good whenever we get more than a glimpse of her in motion.

"Neagley" finally loosens up a little, as various issues are dealt with and packed away, and the characters begin to relate on a more personal level, as people who might be friends. By the end it does manage to suggest — with the team walking four abreast toward the camera in slow-motion — a workable future for the franchise. I would probably watch that show.

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‘NEAGLEY’

Rating: TV-MA

How to watch: Prime Video

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'TOMMY & TUPPENCE'

Rating: TV-MA

How to watch: BritBox

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