Every time I walked by the house it haunted me. The run-down brick house at the top of a hill, window frames rotting, trim crusted with flaked paint. It showed no evidence of life, no evidence of care, but I knew for a fact that someone lives there.   They were almost invisible. I rarely saw them; didn't even know what they looked like or how many lived there. Once in a great while I'd walk by and someone would be riding a tractor cutting the grass in the pasture-like field. With his back to me. One time there were a couple of guys working on a broken-down truck in the yard. One of them knew m