The Dead Girl in 2A by Carter Wilson

Jake Buchannan knows the woman sitting next to him on his business flight to Denver—he just can’t figure out how he knows her. Clara Stowe isn’t in Jake’s line of work and didn’t go to college with him. They have nearly nothing in common apart from a deep and shared certainty that they’ve met before. Despite their best efforts over a probing conversation, both struggle to figure out what circumstances could possibly have brought them together. Then, in a revelation that sends Jake reeling, Clara admits she’s traveling to the Colorado mountains to kill herself, and disappears into the crowded airport immediately after landing.