Velocity - Dean Kootz

Bill Wile is an easygoing, hardworking guy who leads a quiet, ordinary life. But that is about to change. One evening, after his usual eight-hour bartending shift, he finds a typewritten note under the windshield wiper of his car. "If you don't take this note to the police and get them involved, I will kill a lovely blond schoolteacher. If you do take this note to the police, I will instead kill an elderly woman active in charity work. You have four hours to decide. The choice is yours.
"