The 5th Wave (book 1) (Rick Yancey)

On a lonely stretch of highway, Cassie runs. Runs from the beings that only look human, who have scattered Earth's last survivors. To stay alone is to stay alive, until she meets Evan Walker. Beguiling and mysterious, Evan may be her only hope. Now she must choose: between trust and despair, between defiance and surrender, between life and death.