Amy (Jessica Chastain), a compassionate nurse and single mother struggling with a life-threatening heart condition, is stretched to her physical and emotional limits by the heavy, demanding night shift in the ICU. But help arrives when Charlie (Eddie Redmayne), a caring and compassionate new nurse, arrives on her ward. As the two develop a strong and loyal friendship during the long nights at the hospital, Amy feels confident for the first time in years about her future and that of her daughter. But after a series of mysterious patient deaths sparks an investigation that points to Charlie as the prime suspect, Amy is forced to risk her own life and the safety of her children to uncover the truth.