Humans have long been intrigued by the idea of an unknown twin roaming the earth living a parallel lifeline. The term doppelgänger is German for “double goer” and in literature refers to the idea of a character who bears a strong or identical resemblance to the protagonist without being biologically related. The concept can also refer to a shadow self or evil twin borne of the protagonist who exemplifies a sinister side of their personality. Tana French examines the concept of the doppelgänger through Detective Cassie Wilson’s discovery of her undercover alias Lexie Madison in the flesh as a stabbing victim. The journey to uncover the dead woman’s identity finds Cassie reborn into her ghostly double, causing her to lose touch with her professional and personal identity and putting her life in danger.

Cassie’s twin first appears as an undercover identity created by her and Frank. “When I was Lexie Madison for eight months she turned into a real person to me, a sister I lost or left behind on the way; a shadow somewhere inside me, like the shadows of vanishing twins that show up on people’s X-rays once in a blue moon” (52). Cassie’s twin does not fit the traditional mold of an evil double roaming the earth with sinister aims.