“Where are you my white doe? / Fairy tale! / My silent image!” calls the Prince in the last scene of Rusalka, as he runs into the forest—and into the arms of fate. The libretto of Rusalka, Dvořák’s opera of 1901, is based on Friedrich, Baron de la Motte Fouqué’s famous tale of a water sprite, Undine, but with added elements from Slavic myth. Mysterious encounters. Self-fulfilling Freudian prophecies. This opera about imagination is the season opener, in a new production. —L.J.