What do you get when you cross a woman-in-peril thriller with a serial killer study, hospital drama, police procedural, real-life tragedy, and horror movie? The new Netflix film “A Good Nurse” may well be the result, and like other Frankenstein-fitted genre amalgamations, it can be fascinating and frustrating in equal measure.

The woman-in-peril genre, with a prime example being the Joan Crawford classic “Sudden Fear,” thrives on the vulnerability of its female lead; in “A Good Nurse,” Jessica Chastain is our endangered heroine. She plays Amy, a nurse in a New Jersey hospital and single mother with several hazards in her life: a severe heart condition that puts her at risk of a life-threatening stroke, no medical insurance (until she makes a year at the hospital), the potential of losing her job, and financial issues. 

Her biggest threat, though, materializes in the form of a new fellow nurse, Charlie. Initially, Charlie is friendly, even comforting, and when he finds out about Amy’s cardiomyopathy, he vows not to tell their boss or co-workers. He even helps Amy out at home with her two daughters. It’s only when a few patients at the hospital end up dead for inexplicable reasons that she begins to suspect Charlie may be a sinister presence.

Several early scenes with Charlie, played by Eddie Redmayne, present the character as seemingly benign yet with an undercurrent of crazy, as when he places his face close to that of a deceased woman. With Amy’s suspicions of his involvement in the deaths confirmed an hour into the film, the exploration of a serial killer comes into focus, and the bland qualities of Mr. Redmayne’s characterization become central to the movie’s strange pull. 

We want to know more about this character’s motives even as we’re aware that nothing can truly explain such abnormal behavior.

The day-to-day running of a hospital is another element in “A Good Nurse” that gets some screen time. We see Amy and Charlie administer IVs and deal with emergencies, and we also see how hospital management goes into risk-reduction mode when it senses that one of its employees may be at fault in the deaths. This element dovetails with the police procedural plot in the screenplay, as two investigators, played by Nnamdi Asomugha and Noah Emmerich, look into the deaths at the hospital. They are often stymied by a steely hospital executive, superbly portrayed by Kim Dickens.

There’s also the true crime aspect to the story. A few scenes featuring a couple of Charlie’s victims before their deaths, as the nurses interact with them as patients, sketch out the tragedy of his killings. As with the accusations of insensitivity and exclusion that have been lobbed at “Monster: The Jeffrey Dahmer Story” (another Netflix entertainment), “A Good Nurse” isn’t terribly concerned with their lives or the aftermaths of their deaths on their loved ones. 

What the movie keeps returning to, especially once Amy starts assisting the police in their investigation, is whether Charlie will hurt Amy and her family. Also, whether Amy will even survive to see justice served, since her frail heart doesn’t get any better as the movie progresses. Inconsistencies abound, though, regarding her condition, as during the scene in which we see her sprint up a hospital stairwell when there’s really no urgency instead of using an elevator, or when she agrees to the iffy proposition of wearing a wire for a meeting with Charlie at a diner. 

The horror movie quotient is apparent whenever Amy has breathing difficulties, with foreboding music underlining the danger she’s in. Upping the eerie atmosphere, Danish director Tobias Lindholm in his first English-language movie gives the movie the visual appeal of a cadaver with dark-hued, bluish cinematography.

Ultimately, most viewers will stick with this odd mix of genres because they’ll want to know how it ends (if they don’t know about the case already), and because of the acting. Ms. Chastain, fresh off her Oscar win for “The Eyes of Tammy Faye,” gives a reliably terrific performance, by turns fragile and determined. Yet Mr. Redmayne is the one most people will talk about after watching “A Good Nurse.” 

With his boyish face and quiet demeanor, and usually seen in a gray cardigan sweater and blue scrubs, Mr. Redmayne makes for a deeply incongruous serial killer. Much like the movie he’s in, he’s singular and strange.