Some heroes wear capes, but in The Good Nurse, Jessica Chastain’s quiet crusader wears scrubs to stop a murderer. Based on a true story and directed by Tobias Lindholm, the film centers around Amy Loughren (Chastain), a nurse and single mom who slowly comes to realize that her best friend and colleague, Charlie Cullen (Eddie Redmayne), has been intentionally killing patients on the job. Preparing to play a health-care worker during the COVID-19 pandemic carried special significance for Chastain. Speaking with Krista Smith in a new episode of the podcast Skip Intro, she described the lengths to which she and co-star Redmayne went to make sure their performances would be grounded in authenticity.

“Tobias wanted Eddie and I to go to nurs[ing] school, and we had contacted some schools, but there was nothing that they could do,” Chastain said. “So they created a nurse school for us. Day one it was the history of nursing, we learned about Florence Nightingale. We really kind of learned from the bones up. Eddie and I were learning about IVs, we were shooting into mannequins’ arms.”

The two had very different styles, however. “It’d take [Eddie] a long time because he’d be overthinking everything,” she joked. “I just kind of go in and jab the needle.”

Nailing some basic technical aspects of the job — like threading IVs and drawing blood — was crucial for Chastain, who wanted it to look as natural as possible. “So much of Amy is, she loves her job,” she said. “I needed to get to the point that I was just so comfortable doing it that, in scenes, it just felt like she was breathing.”

Chastain also had multiple conversations with Loughren herself in order to really get a sense of what she was going through at the time. The film depicts Loughren’s real-life struggle with cardiomyopathy, a life-threatening heart condition that she lacked the financial resources to treat, even as she saved others’ lives. 

In order to simulate the physical effects brought on by the condition, Chastain would run laps around the sets before a scene, working up a sweat and raising her heart rate. 

“It’s hard to play a person with a heart disease without overdoing it,” said Lindholm, who came up with the idea of having Chastain wear an earpiece so she could actually hear what a faster heartbeat might sound like and know exactly when to play that for the camera. That restraint, Lindholm added, is the real power of her performance. “It was always so subtle and scary.”

For more behind-the-scenes insights into the making of The Good Nurse, tune into this week’s Skip Intro on Apple, Spotify or wherever you get your podcasts.