If you’re already afraid of hospital stays — and really, who isn’t? — watching The Good Nurse is going to be an especially scary experience.

The thing you probably want to know most when watching this true crime Netflix movie is why former nurse and serial killer Charlie Cullen (Eddie Redmayne), currently serving multiple life sentences, murdered at least twenty-nine patients by spiking random IV bags in the supplies cabinet with overdoses of medications like insulin or digoxin, soon to kill whatever unlucky ailing person got hooked up to one of the spiked bags.

But it seems Cullen never said definitely why he did it. It’s possible he didn’t know why himself. In the film, all he states is, “Because nobody stopped me.” And that’s the admirable angle the film takes to redirect your attention throughout to another question: why so many different hospital authorities never investigated or reported Cullen.

He moved from job to job and hospital to hospital for years, garnering suspicion repeatedly when the number of patients “coding” spiked during his period of employment. Then he moved on — sometimes he was pushed on, though always with the agreement that he’d get, at worst, a neutral recommendation — until he was caught, and by that time he’d probably killed hundreds of patients whose strange, sudden deaths were never investigated.

The film makes clear that fear of litigation made his employers take the alarming corporate route of most hospitals being run like businesses: lawyer up and play it cagey time after time. A consistent and appalling lack of responsibility toward patients underscores everything that occurs in the Cullen case.

Another reason Cullen could get away with so much during a sixteen-year murder spree is the substandard care offered in hospitals that are often grotesquely underfunded and understaffed. “The Good Nurse” of the title, Amy Loughren (Jessica Chastain) is good because she keeps trying to supply the attention and empathy so often left out of patient care, such as when she breaks the rules by allowing the elderly husband of a terribly sick woman to sleep in the chair by her bed through the night. Loughren is immediately reprimanded for this by her manager, because the hospital can’t be run like a “hotel” — not when budget cuts mean they’re actually counting coffee filters.

The director, Tobias Lindholm (who cowrote the award-winning Danish hit Another Round), brings to bear all the indignation of a person raised in a country with nationalized health care in filming this tale of a killer hiding in plain sight in a appalling system that’s routinely threatening the well-being of patients anyway. And Amy Loughren is always in danger of becoming a patient herself in the hospital where she toils, because of a severe heart condition that’s soon to put her on a transplant list.

She herself is a contract employee uninsured for the first year of her employment. When she first encounters new coworker Charlie Cullen, she still has four more months to go of trying to calm herself during sudden attacks of rapid heart rate, shortness of breath, and the possibility of a stroke. These are the tense scenes wedged in between the other tense scenes involving her being drafted by investigators into the effort to prove that Cullen is a serial killer, preferably by wearing a wire and getting him to confess to her what he’s done.

She’s drafted because Loughren and Cullen have become friends, bonding over his sympathy for her plight. She’s a single mother with two girls to raise, that all-too-familiar figure in America of the desperate, overburdened worker grinding through day after day, just trying to survive somehow until her grotesquely cruel situation eases up a bit. Cullen offers to help, with every appearance of kindliness, and is soon practically part of the family.

She’s betraying what seems to be the genuinely good part of Cullen in cooperating with the police. The scene when she returns home after meeting with investigators to find Cullen already sitting comfortably with her daughters, who dote on him, is an especially gripping one.

There are only hints in the film about Cullen’s bleak background — specifically the traumatic early loss of his mother, who died in a hospital and was cremated before he was even notified, and his separation from his children because of the efforts of his ex-wife to keep him away from them. Not mentioned are his miserable Irish-Catholic working-class upbringing and his history of severe mental instability, continuous depression, and many suicide attempts.

If you read up on Cullen, you learn that after he was apprehended, he claimed a kind of “mercy-killer” status, wanting to spare patients suffering, especially the horrors of “coding,” going into often brutal “Code Blue” resuscitation attempts — though it’s clear that he killed patients who were recovering or never in any danger of such “coding.” There’s a trace of this left in the film’s opening scene focused on an emergency resuscitation. It’s happening just offscreen, so we can only hear the chaotic and strenuous efforts of doctors and nurses to keep the patient alive. The camera dollies in slowly to a close-up of Cullen’s bowed head and suffering face.

There’s a reason people going into the hospital opt to sign “Do Not Resuscitate” forms.

The most fascinating aspects of this film are found in its broader, contextual approach showing how the acts of a killer are readily disguised by the frequently nightmarish workings of hospitals within a for-profit health care system. Even the greenish-grey lighting in the hospital scenes is typical of horror films. They remind us yet again of the unnecessary dangers and substandard care we endure while just trying to live our ordinary lives.