Keira Knightley in Netflix Mystery

In the interest of full disclosure, I like my shipboard murder mysteries with an all-star cast and at least a soupçon of camp. That makes it hard to top the high-water mark of the 1978 Death on the Nile, with the delicious feast of Bette Davis and Maggie Smith swapping acid-tongued barbs and Angela Lansbury in full dotty-eccentric glory; or 1973’s The Last of Sheila, written by Anthony Perkins and Stephen Sondheim, no less, and featuring the incomparable Dyan Cannon as a stand-in for brash ‘70s Hollywood superagent Sue Mengers. By contrast, Netflix’s The Woman in Cabin 10 takes itself very seriously.

That might not necessarily be a bad thing for readers who loved Ruth Ware’s 2016 mystery novel. But Australian theater and film director Simon Stone’s blandly glossy, capably acted adaptation, co-written with Joe Shrapnel and Anna Waterhouse, is mostly a pedestrian affair that waits until the denouement to crank up the suspense and show some teeth.

Keira Knightley plays Laura “Lo” Blackwood, a respected London investigative journalist traumatized by the killing of a woman who agreed to speak with her for an exposé of NGO embezzlement. While her editor, Rowan (Gugu Mbatha-Raw, wasted in a nothing role), doubts there’s much of a story in it, she agrees to send Lo on the maiden voyage of the Aurora Borealis, a “fuck-off big yacht” owned by Richard Bullmer (Guy Pearce).

The husband of Anne Lyngstad (Lisa Loven Kongsli), a shipping heiress with stage four leukemia, Richard is taking the company’s well-heeled board members on a three-day cruise that will wind up in Norway with a fund-raising gala for the cancer foundation being established in Anne’s name. He wants Lo to come along and cover it to help raise awareness; she hopes the cushy assignment might restore her shaky faith in humanity.

But tension intrudes as soon as she boards the mega-yacht and starts sipping champagne amid the standard — though generally thin — character introductions. Lo and behold (sorry), her photo-reporter colleague Ben Morgan (David Ajala), with whom she had a romantic entanglement that unraveled badly, will be staying in the cabin directly opposite hers. Awkward.

Also on board is the doctor and longtime family associate treating Anne, Robert Mehta (Art Malik); cocky party boy Adam Sutherland (Daniel Ings); high-end art gallerist Dame Heidi Heatherley (Hannah Waddingham) and her pompous toff husband Thomas (David Morrissey); tech titan Lars Jensen (Christopher Rygh) and Grace (Kaya Scodelario), the influencer posing as his girlfriend for optics; plus assorted others. Most are either composites of or departures from the characters in Ware’s novel.

In lieu of “the movie star, the professor and Mary Ann” (if only), there’s recovering addict and guitar-strumming former music star Danny Tyler, played by Paul Kaye as the gone-to-seed love child of Johnny Depp in Pirates of the Caribbean and Gary Oldman in Slow Horses. Coarse and unfiltered, he’s allegedly a dear old chum of suave Richard’s, though the connection doesn’t compute.

There’s the threat of some bitchy, class-divide fun early on as Heidi looks down her nose at Lo, asking her husband, “Why is she in jeans? I feel like there was a dress code.” Lo then makes herself a target of snarky digs by overcompensating for her differences — she’s a Nicholas Kristof type, more comfortable embedding with oppressed Kurdish women — by throwing on a silver sequined number for a casual light supper. So gauche.

But the script has little interest in exploring any potential for incidental humor. Instead, intrigue is planted when Lo is summoned to meet Anne in her cabin the first night. Professing her admiration for Lo’s work “giving a voice to the voiceless,” the heiress reveals that she was the one to request the journo’s presence.

Admitting that her mind isn’t what it was since treatment, Anne asks Lo to look over her speech for the gala, outlining her decision to leave her entire fortune to charity and put the foundation in the hands of “smarter, kinder people.” “Charity without the ego,” coos Lo admiringly.

If you can’t guess the kind of dirty deeds that portends, you need to brush up on your Hercule Poirot. A key piece of casting alone is a tipoff, though the mystery is teased out as to exactly what happened and whether there was a crime at all. The script foregoes the usual pleasures of making almost everyone a suspect — even if more than one person might be in on it.

After an unintended encounter with a furtive woman (Gitte Witt) in cabin 10, the one next to Lo’s, the reporter hears a violent scuffle through the walls, followed by a splash. She rushes onto her balcony in time to glimpse what appears to be a body in the water and a bloody handprint on the wall. But the ship’s mayday alert is called off the next day when a head count reveals that nobody is missing and Lo is informed that cabin 10 was never occupied.

Despite increasingly menacing warnings to back off and stop prying into the lives of rich power players thorny about their privacy, Lo remains determined to get to the truth. This prompts hostility from fellow passengers dismissing her as a nut who imagined everything — even after she has a brush with death in the swimming pool.

Knightley plays all this with intensity, integrity and lots of lip-biting anxiety, making the movie absorbing enough as Lo gets puts through the gaslighting wringer in the glamorously claustrophobic setting. But only in the fraught final stretch, as they get closer to docking and then go ashore for the gala at a scenic coastal location, do other characters have anything vital to do.

Most notably, that includes Witt’s mystery woman and Richard’s head of security Sigrid (Danish actress Amanda Collin, who I spent a scene or two convinced was Sandra Hüller). Ajala and Malik’s characters also come into play in more strategic ways, though most of the assembled party is too colorless to make them all that compelling.

Like much original streaming fodder, The Woman in Cabin 10 will be perfectly adequate entertainment for multitasking viewers, though it’s a bit plodding, even at 90 minutes. Stone (who directed The Dig for Netflix) does a competent job connecting the dots, but where’s the sense of style of these rich folks? Or the décor flourishes of a squillion-dollar yacht that’s tasteful to a fault? We’ve seen better f**k-off boats and chic wardrobes on Succession.