Yellow Slicker

Duncan's life of privilege takes a horrifying turn late one night when he drives around a bend, sees a flash of yellow, and feels a sickening thud. He does check, but confused and panicked, he leaves the scene.
A day later, he notices a dent in the fender and finds a torn piece of yellow fabric clinging to the bumper.
Hours become days, days become weeks. No one comes forward.
But the strange signs and messages can't be coincidence and Duncan comes to realize there is a witness.
Who are they?
What do they want?
What will happen to his reputation and the life he has built if this gets out?
And...what can he do to stop it?