In Tobias Lindholm’s “The Good Nurse,” the sharply-refined lead performances from Eddie Redmayne and Jessica Chastain are so strong that they make viewers forget about a screenplay that doesn’t always live up to their work.

Written by Krysty Wilson-Cairns (“1917,” “Last Night in Soho”) and based on the book by Charles Graeber, the film focuses on the crimes of Charles Cullen, a nurse who, over the span of sixteen years, confessed to murdering close to forty patients while working at different hospitals in the New Jersey and Pennsylvania areas. Authorities estimate the number of victims may have been in the hundreds.

The film is certainly a true-crime drama, as Wilson-Cairns’s screenplay takes the viewer into the twisted mind of the murderer while balancing a character piece. While the picture never fully finds its dramatic stability, it’s far from devoid of interest.

Jessica Chastain finally returns to giving great performances (her Oscar-winning turn as Tammy Faye Baker was solid but came through more as imitation, however spot on an imitation it was). The actress is perfect playing Amy Loughren, a nurse working for a New Jersey hospital, a single mom with a heart condition and shaky insurance, Amy pushes herself too often due to the understaffed hospital.

Enter Charlie Cullen, a young male nurse who alleviates some of the workload. So thankful is Amy to have a partner that she is blinded to his strangeness and cannot see how there is something off about this very dangerous man.

Patients begin to die. The hospital’s director (a Kim Dickens in top form) goes to the authorities regarding the death of one of Amy’s patients who overdosed on too much insulin.

The motivation of Dickens’s character is dubious, as she is more concerned with liability issues.

The authorities send two investigators (Noah Emmerich and Nnamdi Asomugha) who, during their investigation, find out about Cullen’s reputation and chase down a string of unexplained deaths in the nine hospitals where he used to work.

As the investigation continues and the rumors around Charlie Cullen begin to swell, another patient in Amy’s care dies.

Chastain and Redmayne play off one another, as Amy responds to Charlie’s kindness Chastain disappears into her role–that’s good acting!

Eddie Redmayne is a fine actor (if occasionally too mannered) and does very well here. Cullen is a dangerous man, but Redmayne doesn’t play it expectedly sinister. The performance is focused and disturbingly real. Forgiving the histrionics Redmayne lets loose near the finale, this could be the actor’s most affecting work.

Director Tobias Lindholm keeps the film engrossing for a while, until the attempt at social commentary regarding a possible bureaucratic cover-up hits a dead end.

Presenting some interesting arguments, the film opens doors to an examination of an American health care system that cares only for profit. Sadly, Lindholm tanks all interest by turning the final act into a standard thriller with no thrills to speak of, breaking the spell of the first half.

Biosphere’s atmospheric score helps, keeping a hold on the darker tone that mirrors the subject matter while Jody Lee Lipes’s camera closely tracks the pained faces of Amy (beginning to see emotional cracks in her new friend) and Charlie. Lipes’s work enhances the creepiness of this man, who roams the hospital hallways, moving like a cold wind in the shadows, always staring intently at the patients.

While I cannot fully praise the film, as it bogs itself down with its standard Hollywood styled pulp wrap-up, “The Good Nurse” is an attention-grabbing watch for a good portion of its running time.

When it all begins to fall apart cinematically, performances by Jessica Chastain and Eddie Redmayne are the anchor that will keep you watching “The Good Nurse.”