Maria Nieves and Juan Carlos Copes are passionate about Argentine tango. They have been dancing together for 40 years and are among the best-known dance pairs in the world. Copes was once heard to say that if he had not found Nieves--someone to whom he is remarkably attuned--he would need four different partners to fully explore the tango's expressive spectrum. Anyone who has ever done pairs dancing will understand just how difficult it is to forge a merger out of differing styles and capacities, while coordinating movements with near perfection in space and time.