In the horrific opening moments of The Good Nurse, we are shown just how quickly the world around someone can go from compassionate to cruel. From outside a hospital room, we see a patient crashing, as the machines go wild, beeping out its warning signals. First to assist in the room is Charlie Cullen (Eddie Redmayne), a nurse who comes to the patient’s side, calling for help, as the patient’s life is clearly in danger. As other doctors and nurses come in to aid, Charlie slowly moves to the back of the room, observing the scene. His attempt at kindness slowly fades from his face, as he adopts a more careless, inhuman look, watching the destruction he’s helped cause. In a job that asks him to do no harm, Charlie has realized just how much harm he can do and revels in this type of destruction.

A few years later, Charlie moves to a new hospital where he meets Amy Loughren (Jessica Chastain), a single mother who discovers she needs a heart transplant, yet she still has a few more months before she can get health coverage at her job. Amy is a great doctor who fights against the bureaucracy of her hospital to help those in need and caring even when it threatens to put her own life at risk—as when she moves a patient in bed by herself as she struggles to catch her breath. Charlie and Amy quickly strike up a new friendship, with Charlie agreeing to help Amy until she gets health coverage. But when patients start dying mysteriously, all the facts start to lead to Charlie, and a pair of cops (Noah Emmerich and Nnamdi Asomugha) start coming around and asking questions, Amy does what she can to once again help her patients, regardless of the cost.

Directed by Tobias Lindholm, the co-writer of Another Round and director of A War, and written by 1917 and Last Night in Soho co-writer Krysty Wilson-Cairns, The Good Nurse is an unnerving and tense drama that is terrifying in its simplicity. Cinematographer Jody Lee Lipes (Manchester by the Sea, I Know This Much Is True) knows how to light a film in a way that feels distressing even in the positive moments, and the haunting score by Biosphere leaves the audience in a continual state of unease, even when there’s nothing to fear.

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Wilson-Cairns’ screenplay, which is based on a true story, is largely a battle of wills, dealing with who knows what and when. Once we start to see the pain Charlie can cause, The Good Nurse becomes about why someone who can put on such a kind face could do such atrocities. Wilson-Cairns does this by showing us this hospital through Amy’s eyes instead, as we have empathy for the patients that come through and put their lives in her hands. We see how even the simplest acts of tenderness can mean the world to someone during one of the worst times in their lives, and how just a little care can go a long way. Even before we know what Charlie can do, we can already see the difference in both Charlie and Amy’s way of doing their jobs, and how even that little extra goodwill can mean so much.

The Good Nurse is a film that needs two fantastic performances to make this concept effective, and both Redmayne and Chastain are doing excellent work here. Through Chastain, we see the quiet affection that her job requires, and once she discovers the truth about Charlie, she’s able to use this tool to draw him in closer and attempt to get him to confess. Chastain gives a wonderfully subtle performance, as we can see the horror in her eyes when she deals with Charlie after discovering his secret, but she also knows that she has to keep her cool and attempt to not let on what she knows. For a person whose work is largely reliant on understanding and sensitivity, Charlie’s lack of both makes him an understandable challenge for her.

But truly impressive is Redmayne, in what might be his best performance yet. Charlie almost has a Norman Bates-ian quality to him, as the audience understands how someone could be drawn to his friendship and quiet hospitality that he gives to some. Charlie might be pure evil, but that doesn’t mean he doesn’t care for Amy, and his true sinister nature, mixed with his general attempts to be a good person with Amy is a difficult balance to maintain. Charlie is a slow-burn of a character and as the walls start to close in on him, Redmayne is allowed to let loose in a way that is both powerful and horrific. Redmayne plays Charlie like a man hiding his true nature, and once we see what dangers lie within, it’s impossible for him to put that beast back in its cage. But again, it’s that mixture of likability and the sheer indifference for others that makes Charlie such a potent and believable monster.

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While The Good Nurse explores how the hospital administrative boards could allow someone like Charlie to get away with his crimes and even thrive in his ability to kill, it never quite digs as deep into this side of the story as it maybe should. The relationship between Charlie and Amy is so fascinating that it takes up the majority of the runtime, while the police investigation into the hospital coverup of what is actually going on gets pushed to the back burner.

The Good Nurse is a shocking drama that seeps under your skin with its ferocity and terror. Yet Lindholm makes this story about a disturbing individual into a film about how important kindness and consideration for others can mean in the larger scheme of things. Whether through assistance when cold red tape of healthcare gets in the way of people in their time of need, or how the most basic amount of human decency can change a person’s outlook, The Good Nurse shows that even the smallest light can shine in the darkness.

Rating: B+

The Good Nurse is now streaming on Netflix.