Tertuliano Máximo Afonso is a divorced high school history teacher who spends his nights reading about Mesopotamian civilizations. One day Tertuliano rents a movie recommended by a colleague; he sees a bit actor who looks exactly like him. Tertuliano becomes obsessed with meeting the man and spends weeks discovering the actor's name. He sends a letter to the production company, from his girlfriend's address and posing as a film student, in order to be put in contact with the actor. His relationship with his girlfriend, Maria da Paz, suffers because he refuses to disclose his motives to her. After receiving the actor's phone number and address, Afonso stalks his double, António Claro, eventually calling him. Claro's wife mistakes Afonso for her husband on the phone. Initially, António Claro dismisses Afonso and refuses to meet, but later contacts him and agrees. They decide to meet at Claro's country home in a week.
Afonso buys a fake beard and drives out of town to meet Claro. Upon arrival, the men strip down and find that they are indeed identical, and they discover they were born on the same month, day, and year. Their voices are exactly the same, and they share identical scars and moles. Before Afonso leaves, Claro asks him to clarify one more thing: the exact time he was born. He wants to know which of them is the "original," and which the double. Afonso says that he was born at two in the afternoon. Smugly, Claro informs Afonso that he was born a half hour earlier, making him the original. Afonso gets up to leave, saying that he has the small compensation of knowing that Claro will be the first to die, and he will become the original in turn. To this, Claro responds, "Well, I hope you enjoy those thirty-one minutes of personal, absolute, and exclusive identity, because that is all you will enjoy from now on." The men agree that they have no reason to ever meet again, and Afonso leaves.