Based on a true story, the movie features nurse Amy Loughren (Jessica Chastain). She balances her career with her role as a single mother. Now, she learns she has a life-threatening heart condition that requires a transplant. She finds herself without health insurance because she hasn’t worked at the hospital long enough. So, she doesn’t reveal her diagnosis to her bosses, but she does confide in a co-worker, Charles Cullen (Eddie Redmayne), another nurse.

Charles helps her with her patients and her children. Amy doesn’t know that the death of one of her patients is being investigated because of a large amount of insulin in the patient's system. The hospital reports the death to local authorities to counter their legal liability.

During their investigation, Tim Braun (Noah Emmerich) and Danny Baldwin (Nnamdi Asomugha) discover similar stories about at least 29 patients at nine other hospitals where Charles worked. These hospitals chose expediency to avoid lawsuits. However, when a second patient of Amy’s dies, she helps the authorities.

She talks to a friend at one of the other hospitals and then talks to Charles as the detectives monitor the conversation. Charles becomes agitated, so the detectives arrest him. Charles doesn’t confess until Amy talks to him again. Without Amy’s cooperation, Charles may have moved on again.

Charles receives 18 life sentences, and Amy gets her heart transplant.