After his 2003 arrest, registered nurse Charlie Cullen was implicated in the deaths of as many as 400 patients, making him the most prolific serial killer in American history. Based on police records and conversations with Cullen himself, Charles Graber's tense but thought-provoking portrait—inspiration for the 2022 Netflix film starring Eddie Redmayne—follows the homicide detectives who worked to crack the code on Cullen's crimes, and profiles nurse Amy Loughren, who had to choose between protecting her friend Charlie and stopping a potential killer.