In the first chapter of The Woman in Cabin 10, Laura “Lo” Blacklock wakes up in darkness, bleary-eyed after a night of heavy drinking (“I really have to stop drinking midweek”) to find a masked man wearing latex gloves robbing her apartment; he slams a door in her face, injuring her cheek, and locks her inside her bedroom before escaping with her handbag. It’s a deeply traumatic experience, and readers of Ruth Ware’s 2016 mystery soon learn that Lo has other troubles that add to her frequent anxiety (for which she’s taking medication), including a fraught relationship with her jet-setting photographer boyfriend (she’s got commitment issues) and an unsatisfying job “cutting and pasting press releases” at the London-based travel magazine Velocity.

None of this stops Lo from going on the maiden voyage of the Aurora Borealis, a small cruise liner owned by the wealthy Lord Richard Bullmer, who’s onboard along with his terminally ill wife, Anne. Lo’s assignment is to network with various rich folk on the sea voyage to Scandinavia and write a puff piece for Velocity. However, she becomes entangled in a murder mystery on her first night, when she awakens, half drunk, to hear “the kind of splash made by a body hitting water.” A new film adaptation, starring Keira Knightley and Guy Pearce, premieres on Netflix on October 10.

Lo is sure that the person thrown overboard was a passenger staying in the cabin next to hers—an agitated young woman wearing a Pink Floyd T-shirt, from whom Lo borrowed some makeup. However, when she alerts the crew, they insist that no one was staying in Cabin 10, which is now vacant, with no sign of recent occupancy. No one believes Lo’s story—after all, she’s sleep-deprived, hungover, and generally on edge. But she knows what she witnessed, and she’s determined to get to bottom of the mystery; to that end, she reluctantly enlists the help of a fellow journo onboard—Ben Howard, who also happens to be her ex-boyfriend.

Despite the superficial Agatha Christie–like trappings of the setup—a murder on a cruise ship, and a cast of (mostly) upper-crust suspects—Lo is no Jane Marple or Hercule Poirot. Indeed, she’s barely functional, spending much of the novel drunk, hungover, exhausted, and/or on the verge of panic. (It’s no wonder that she vomits multiple times over the course of the story.) She stumbles through the investigation in a scattershot manner, making little headway; it’s only toward the end, when she’s kidnapped and imprisoned in the depths of the ship by a key character, that she finally pieces things together.  

Lo’s fierce determination—not her detecting skills—makes her an intriguing protagonist. Although nearly everyone condescendingly insists that she’s imagining things, she refuses to stop searching for the truth. Her offbeat relationship with her ex, Ben, is also unusual for a thriller; he is, quite frankly, a jerk, and she has no interest in rekindling their romance, but he’s always firmly in her corner, nonetheless; he believes her when all available evidence indicates that she’s delusional.

Although the characterization is interesting, other aspects of The Woman in Cabin 10 disappoint. The mystery feels strangely underdeveloped; there’s a notable lack of red herrings (especially ironic in a seagoing whodunit). The novel never gets its bearings as a thriller, either, as the reader never feels that Lo is in real danger—until, of course, the aforementioned abduction late in the story. The final resolution feels like an afterthought, with a significant character’s demise taking place off page.

The new film version, directed by Simon Stone (The Dig), mistakenly tidies up Lo’s messy life. She’s no longer a second-stringer at a travel mag; now, as portrayed by Knightley, she’s a star investigative reporter for the Guardian, known for her stories on oppressed women around the globe. If she has a drinking problem, it’s offscreen, and if she’s struggling with mental health issues, there’s no indication. That break-in at the beginning of the story? Never happened. She doesn’t even have a current boyfriend to cause her angst. As such, the movie’s Lo is much steadier than her literary counterpart; indeed, one wonders why anyone would ever doubt her. That said, she’s also a much blander character—a stock hero of the type that viewers have seen before in countless thrillers.

The story, however, gets a significant upgrade, weaving in a much clearer motivation for the central crime; several tense moments of peril, including one in which Lo nearly drowns in a covered pool and another in which Ben struggles with a corrupt individual wielding a deadly hypodermic; and a lively climax, set on land, during which the main villain takes a hostage, resulting in a tense standoff. The performances are also fun throughout: Guy Pearce, as the wealthy Richard Bullmer, combines the superficial manner of a game-show host with a serpentine shiftiness; and Star Trek: Discovery’s David Ajala gives Ben a smooth charm that enlivens his every scene. Indeed, Ajala feels a bit underused, as do The Walking Dead’s David Morrissey and The Gentlemen’s Kaya Scodelario, both delivering entertaining performances as shallow, rich passengers. Knightley, too, brings an appealing energy to Lo—although viewers may wish that she’d been given the chance to play the book’s version of the character, who barely manages to keep her head above water.

David Rapp is the senior Indie editor.