Come and Find Me By Hallie Ephron

Computer expert and reformed hacker Diana Highsmith has not ventured beyond her home for more than a year—not since that fateful climbing vacation in Switzerland took Daniel’s life. Haunted by the sound of Daniel’s cries echoing across the gorge as he fell, Diana cannot stop thinking about the life they’ll never have—grief that has transformed her into a recluse.
Diana doesn’t have to shut herself off completely from the world, though; she and Daniel’s best friend run a thriving Internet security company. From her home, in her pajamas, Diana assesses security breaches, both potential and real, and offers clients a way to protect themselves from hackers—the kind of disruptions Diana herself used to create. Once Diana has a game plan she is able to meet with clients in OtherWorld, an Internet-based platform, using Nadia, an avatar she created for herself. Diana knows she’ll have to rejoin the “real world” eventually, but right now a few steps from her door each morning is all she can handle.
When Diana’s sister goes missing, however, she is forced to do the impossible: brave both the outside world and her own personal demons to find her sister. 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.