The first episode of Mr. Mercedes, two weeks ago, opened with a car used as a weapon, driving into a helpless crowd – a scene televised days before a similar horror played out for real in Charlottesville. Last week, episode two ended with another chilling scene, but this time it was shocking, and memorable, because of its deliberate and well-aimed profane bluntness. For two episodes, the vehicular villain played by Harry Treadaway had badgered, by computer emails and other means, the now-r