J.D. Foster is an Earthman on shore leave in the spaceport city of Pharagonesia. It's a crazy day in the city, as the locals are celebrating Mutation Day. And it's a crazy day for J. D. Foster, as he's about to experience his first glass of "koks"! Earthmen and koks, they don't mix too well, with the result being more than a little . . . messy.