It was 1969, at the Paris Conservatoire, when everything changed for a pair of strong-willed, piano-playing sisters from France named Katia and Marielle Labèque. They were practicing a thorny two-piano work, Visions de l'Amen, by Olivier Messiaen, one of the school's teachers and by then a legendary composer. He heard the sisters play and asked if one of them would like to record the piece with his wife. They refused, saying they had already decided to stick together as a piano duo.