Theo’s investigation into Alicia’s life, paired with early clues about trauma and external manipulation, sets the reader up to blame outside forces for her silence. But when her diary exposes inner turmoil and buried truths, the reader realizes they’ve been misled.
Dupin is introduced as a creature of romance (reading too many vampire novels), which makes us feel wiser than him. But then, "Dupin turns and reads our mind" and then explains how he does it.