Eight O'Clock, at Your Place(1995)

Javiera and Antonio are a young couple with two daughters and another on the way. But beneath the superficial tranquillity of their marriage hides a passionate relationship between Antonio and his wife's sister, Antonieta. The love triangle begins to lose its delicate balance when Antonieta loses her purse. A mysterious voice on the telephone extorts the lovers, moving them to take unusual actions and to confront one another with blame and doubt, ultimately forcing them to explore the true value of their relationship.