Disney Frozen Polar Nights: Cast Into Darkness

The Snow Queen, Elsa, has been spending more time in Ahtohallan. There, she discovers a multitude of memories--happy memories, sad memories--all connected to no one she knows. This truly gives credence to Olaf's theory that water has memory. When she returns the next day, some of the memories are gone. What, or who, could have done that?
Meanwhile, Anna, queen of Arendelle, has begun trade talks with the neighboring village. But Olaf notices that the villagers seem to really be bickering. "This can be a sign of forgetfulness!" he announces to anyone who will listen. After all, forgetting things does make one annoyed and angry.
Anna and Elsa join forces to determine what is going on. Who can be taking the memories and for what purpose? Together they recall an old bedtime story their parents read to them to keep them in bed. The story warned them about a draugr--an undead creature that steals memories in an effort to make others forget the misdeeds the draugr committed when it was alive.
Is it possible that Elsa inadvertently unearthed memories of a draugr, and thus unleashed the monster upon Arendelle? Did she discover a secret that was supposed to remain forgotten forever?
Can Anna and Elsa discover the truth of the women in the legend before more memories disappear, before everyone in Arendelle and the neighboring village forgets who they are and gets lost in the darkness of their minds, and the Polar Nights descend upon them forever...