In a museum where her father is arranging a sword exhibit after her mother's death, Ophelia looks though a keyhole, being curious, and sees a boy. Dressed in very old fashioned clothes. And prisoner.
She is needed to rescue him. Because he needs to give a sword to the person who will use it against the Snow Queen. And he's been there three hundreds years, and the Winter Clock shows there's only three days left.
This involves the need to not tell ghosts too much, that she can still count how many hours since her mother died, her sister Alison wearing an exhibit piece, the boy's back story, misery birds, sardines, a room full of teaspoons, a foolish king, dinosaur bones, and more.