From the Man Booker-shortlisted author of Autumn, the highly anticipated second novel in the acclaimed Seasonal quartet, which both continues the arc of the series and is also an extraordinary stand-alone read.           Winter. Bleak. Frosty wind, earth as iron, water as stone, so the old song goes. And now Art's mother is seeing things. Come to think of it, Art's seeing things himself.     When four people, strangers and family, converge on a fifteen-bedroom house in Cornwa