Cameras follow Aaron Roach Bridgeman as he hears from the families of people who died after being struck just once by an assailant, and investigates the science behind the violence to find out exactly how a single punch can kill. He also tracks down the perpetrator of one of these attacks to get his side of the story, and brings him together with the mother of the man he killed to find out if she can ever truly forgive him for the death of her son.
