The Vacation by Shirley Penick

Andrea Clementine has a wonderful vacation planned. Nine whole days away from work, from home, from everything but fun. Right up until her car conks out, not even halfway to her destination. Her vacation is ruined, and she’s stranded on the side of the road.
Carl Ray Black is on his way to a conference when he sees a familiar car stopped not quite all the way onto the shoulder. He can’t leave the only woman he’s ever loved abandoned, even if she does hate him with the heat of a million suns.
When they discover they are bound for the same location, Carl Ray offers her a ride. Andrea would ride with a serial killer to start her vacation, as planned. Can they spend five hours in the car together, alone, without murder being committed?