The Driver's Seat

Lise is thin, neither good-looking nor bad-looking. One day she walks out of her office, acquires a gaudy new outfit, adopts a girlier tone of voice, and heads to the airport to fly south. On the plane she takes a seat between two men. One is delighted with her company, the other is deeply perturbed. So begins an unnerving journey into the darker recesses of human nature.

Synopsis from Open Library.