A commonality for most of the characters in Two Can Keep a Secret is their close connection to a violent crime. For many of these characters, the debilitating effects of post-traumatic stress and survivor’s guilt have long-term and devastating effects. Sadie Corcoran blames herself for her sister’s disappearance but never articulates her trauma, leading to a strained relationship with her mother, a history of substance abuse, and teenage children who have dealt with the stress of stepping into the role of parent far too often. The fact that she was losing her virginity the night that Sadie disappeared adds to this trauma. For Daisy Kwon, her attraction to Declan at the time of Lacey’s murder makes her feel complicit in a betrayal that can never be undone, and her breakdown and return home are the direct consequences of not dealing with that pain.

These are the most obvious effects, but there are many others: Nana is hyper-protective of the twins while being hesitant to open up around them, for example, and the town as a whole struggles with its image. The book takes a big-picture, psychological view of violent crime, such that solving the mystery and emotional healing are inextricably linked.