The third season of “The Sinner” starts with a simple car crash on a country road in the middle of the night. What seems like a routine investigation for veteran detective Harry Ambrose (Bill Pullman) opens to reveal a dark and twisted relationship between two former college friends that reverberates through the leafy suburb of Dorchester, New York. It also confirms for Ambrose, afflicted by sciatica and bothered by some family tensions, that retirement is out of the question.