One Rainy Night - Richard Laymon

The strange black rain falls like a shroud on the small town of Bixby. It comes down in torrents, warm and unnatural. And as it falls, the town changes. One by one, the inhabitants fall prey to its horrifying effect. One by one, they become filled with hate and rage.and the need to kill. Formerly friendly neighbors turn to crazed maniacs. A stranger at a gas station shoves a nozzle down a customer's throat and pulls the trigger. A soaking-wet line of movie-goers smashes its way into a theater to slaughter the people inside. A loving wife attacks her husband, still beating his head against the floor long after he's dead. As the rain falls, blood flows in the gutters—and terror runs through the streets.