The Crystal Cave (S03E05)

After an unforeseen encounter with the mysterious old sorcerer Taliesin, Merlin is taken to a crystal cave where he catches a glimpse of what the future holds. This revelation, however, quickly reveals itself to be a curse when he is horrified to witness Morgana plotting to kill Uther. Determined to prevent this dark fate, Merlin realizes that altering destiny is fraught with peril, and his attempts lead to disastrous outcomes. With Camelot engulfed in sorrow, Merlin must find a way to alter the course of fate and rectify the chaos he has unleashed, or risk losing everything.