Even before the events in the supermarket, Jim Ironheart should have known trouble was ing. During the night he dreamed of being pursued across a field by a flock of large blackbirds that shrieked around him in a turbulent flapping of wings and tore at him with hooked beaks as precisely honed as surgical scalpels. When he woke and was unable to breathe, he shuffled onto the balcony in his pajama bottoms to get some fresh air. At nine-thirty in the morning, the temperature, already ninety degrees, only contributed to the sense of suffocation with which he had awakened. A long shower and a shave refreshed him. The refrigerator contained only part of a moldering Sara Lee cake. It bled a laboratory culture of some new, exquisitely virulent strain of botulism. He could either starve or go out into the furnace heat. The August day was so torrid that birds, beyond the boundaries of bad trams