After suffering a breakdown from her brutal divorce, airline pilot Claire Winslow is rebuilding her life with her five-year-old daughter. Just as she's finding her footing, an online romance spirals into a chilling nightmare. Her first date with Evan goes terribly wrong, and he soon begins stalking her, showing up outside her home and even her daughter's school.

After nearly a week of no sightings of him, Claire dares to believe maybe he's moved on. Relieved, she puts her focus on her upcoming flight-the first chance she's had to prove herself since she was put on leave. Then, on a layover in Boston, Claire spots Evan at her hotel. She goes to the police, but with no real name and nothing traceable online, they say there's nothing they can do.

When Evan boards her flight wearing a pilot uniform and takes the jump seat just before takeoff, Claire is convinced he's there to kill her-or take the plane down. But after her recent breakdown, the question becomes: is she right...or unraveling all over again?