A novel that wears its Agatha Christie antecedents entirely too obviously becomes a Keira Knightley star vehicle in “The Woman in Cabin 10,” a film whose producers were clever enough and careless enough to cast Guy Pearce as her foil.

There are two ways things can go when you put the estimable star of “Memento” and veteran heavy of “The Brutalist,” “Brimstone,” and many other villainous turns (He was even an “Iron Man” foe.) in your movie. He’s carried that baggage so well that the moment we see him in a thriller we figure either he’s whodunit or he’s a red herring tossed in to obscure the real killer.

Ruth Ware’s book updates the “Death on the Nile” formula for the age of oligarchs, and the screenwriters tap into the actual predelictions of ultra richies like Zuckerberg and Bezos — who compete to see who can build the priciest yacht, and then load it with fellows swells for ski trips or cruises to see the Northern Lights.

Knightley plays a reporter sent to document a seriously pricey charity cruise aboard a rich couple’s yacht, lazily-named the Aurora Borealis. Lisa Loven Kongsli plays a Norwegian shipping heiress who is dying of leukemia and has it in mind to donate a vast fortune to cancer research upon her death.

But who is heiress Anne Bullmer’s husband? The charming and faintly-patronizing Richard. When you cast Pearce in that part Richard instantly takes on sinister overtones.

Guardian newspaper reporter Laura Blacklock, “Lo” to her editor (Gugu Mbatha-Raw), was traumatized by her last story about a non-profit heroine murdered right in front of her after providing her evidence for that story. She needs a break. A short sail from Britain to Norway on a mini-cruise-ship-sized motor yacht to document a generous act and profile the woman making it would seem just the ticket.

But among those rich acquaintances — Michael Morrisey and Hannah Waddingham play a titled couple, Paul Kaye a swaggering, disolute rocker, Art Malik is a rich doctor friend of the Bullmers, Kaya Scodelario a rich guy’s trophy escort, etc. — is a photographer, Laura’s most recent ex, Ben (David Ajala).

Laura’s just started to try and fit in with this lot when she stumbles into the cabin next door and spies a blonde fresh out of the shower. She’s begun to accept that she’ll never fit in here when she hears a muffled, heated argument and a loud splash later that night.

Man overboard! Or woman overboard!

The vast crew springs into action, but there is no swimmer or body. Cabin 10? There is no one rooming there. That bloody palm print detail-oriented Lo spied? It’s gone.

The doctor is quick to suggest PTSD. The rich folk dismiss her as an “attention” you-know-what.

“I’m not imagining this.”

Confiding in her ex is a non-starter. She’s making waves and “these people run the world,” Ben warns.

But the reporter in her won’t let it go and the “investigation” begins, with the captain and owner Bullmer submitting to many a demand.

“I need to look at the CCTV!”

Knightley does justice to the doggedness one used to associate with journalism and the guarded contempt such people used to treat the world’s robber barons. We believe Laura’s discomfort in this world and even the peril she comes to feel she’s in.

But the plot rather lets Knightley and the character down, with one murder attempt so widely witnessed and calculated that nobody save for someone in a vested interest wouldn’t see it as such.

The casting makes us wonder if the screenwriters watched old episodes of TV’s “Columbo,” where a villain is ID’d in the opening act with the story about the heroine unraveling “your one mistake.” Then again, we figure, “They couldn’t be that obvious, could they?”

The action beats — chases and struggles to the death — play. But the finale is so hoary it’s covered in mold, almost laughably old-fashioned.

There’s too little “Is she just imagining this?” doubt, too few scenes for Pearce to tip us about whether he’s playing a killer or just someone everyone expects to be the killer.

They assembled a cast worthy of a “Death on the Nile” variation set in a fjord. But director and co-writer Simon Stone, who did a fine job with Carey Mulligan’s “The Dig,” is utterly at sea in this genre.

Rating: R, violence, profanity

Cast: Keira Knightley, Guy Pearce, David Ajala, Gigge Witt, Art Malik, Kaya Scodelario, Michael Morrissey, Daniel Ings, Paul Kaye, Lisa Loven Kongsli, Gugu Mbatha-Raw and Hannah Waddingham

Credits: Directed by Simon Stone, scripted by Joe Shrapnel, Anna Waterhouse and Simon Stone, based on a Ruth Ware novel. A Netflix release.

Running time: 1:33