Michel Foucault book

The copy of Foucault's Madness and Civilization that Alex lends to Lydia in the first flashback serves as a symbol of her realization that she might be better off with Zachary instead. Christine comes home and finds Lydia struggling to read and understand the book, most likely in order to further her relationship with Alex. She tells Lydia that Zachary has feelings for her and Lydia, likely contemplating the gap in intellectual interests between herself and Alex among other disparities, decides to pursue Zachary instead.