As the protagonist of this story, Polly is critical to all the threads of the plot, and is the person whose point of view remains steady throughout the novel.
The book begins when she is nineteen, lying with an open book on the bed in her Granny's house, knowing she should be getting up to pack her things to start another year of college, but somehow bemused by the way the book kept reminding her of things she could almost remember, but which made no sense. The first story in the book was about a man with two sets of memories, which makes her very uneasy, because she almost remembers reading the same book many years ago, but there seemed to be stories missing from it now.
As Polly struggles to figure out what is wrong with her, or her memories, or the book, she suddenly remembers the event that started a whole set of adventures that she seems to have forgotten -- a funeral that she crashed back when she was ten, playing make-believe games with a friend she seems somehow to have forgotten, and the people she met because of doing that one thing so long ago. That is how Fire and Hemlock begins, and the adventures that form the nucleus of these lost memories form the plot of the novel.