Although known as one of the most scrupulously accurate of the "hard science" writers, someone careful to always get the scientific details right, Hal Clement also has a rich and lively imagination, especially when it comes to alien lifeforms, and he has created some of the most memorable alien characters in science fiction. Clement's outdone even himself in the suspenseful novella, Exchange Rate, in which harried human explorers (under pressure in more ways than one!) must try to figure out the lifeways and motivations of some extremely strange and enigmatic alien creatures on one of the strangest planets ever portrayed in science fiction - and do it all before the clock runs out. Exchange Rate was chosen for inclusion in the Seventeenth Annual Collection of The Year's Best Science Fiction.