A prisoner of grief, haunted by the death of her husband on a climbing vacation, Diana Highsmith has not left her house in more than a year. But she hasn’t retreated from the world completely. A computer security expert, she runs a thriving Internet company helping clients protect themselves from hackers—the kind of disruptions Diana herself used to create.

But the security and safety of her cocoon is breached when Diana’s sister disappears. To find her, Diana must do the impossible brave both the outside world and her own personal demons. As one step outside leads to another, Diana soon discovers that she is following a trail fraught with danger—and uncovering a web of deceit and betrayal, both online and real-life, that threatens not only her sister’s life, but her own.