Tonight’s two-hour episode expands to make room for a central plot sure to appeal to all the kids whose hearts were warmed by Frozen: like Elsa in that hit animated version of The Snow Queen, Emma (Jennifer Morrison) begins to isolate herself from her community because of fears that her magical powers might bring harm to someone near and dear to her. Meanwhile, this show’s actual, evil Snow Queen, played by Elizabeth Mitchell from Lost, makes herself an even more chilly presence this week.