It's All Hallow's Eve, and the Motherwell sisters, Lili and Cecile, have invited their musicologist patrons, the Brunswick sisters, to attend them on this crucial day. All their lives, Lili and Cecile have practiced on their pianos, to the exclusion of everything else. Their interpretations of Mozart, as the impresario Mendel says, are "too impeccable, too irreproachable," there is "too much politeness, too much purity, not enough passion." They wish to discuss something hidden in their basement--someone has strayed from their score, someone has improvised, the hands of the clock need to be turned back.