The book Le Droit Penal Primitif by Emile Garcon explores the primitive legal systems of ancient societies discussing the origins of penal law justice and the role of family units in administering justice. It challenges the notion that early societies lacked a formal legal system drawing parallels between ancient legal practices and modern international relations. The book also delves into the evolution of penal law reforms introduced by the Revolution principles of punishment and challenges faced by the modern penal system.