Faca de Dois Gumes (1989)

Paulo is a rich lawyer who has a happy and comfortable family life, with his kid and very loyal to his wife. But when he finds out that the woman is cheating on him with his business partner and best friend, he decides to execute a perfect plan that involves murdering both and easily getting away with murder. However, Paulo's plans are about to be ruined due to some unpredictable factors involving powerful people, plenty of money, the kidnap of his son and a tenacious inspector following his steps.