Every action causes a reaction. Newton's 3rd law does not only explain the relationship between bodies and "momentum" in classical mechanics, but also human relationships and the "momentum" that characterizes them, in general. Relationships with others and with ourselves. The relationship between the present and the past. The relationship between the perpetrator and the victim. Family dramas, love affairs of loyalty and infidelity, serial killers, crimes of honor, passion, revenge, punishment, necessity.