Iceworld — Hal Clement

As the planet gleamed in his viewport, Sallman Ken could not believe that such a bleak and icy globe could have produced intelligent life. Yet when the expedition had sent in unmanned landers, that was what it had found. Some sort of native alien, surviving on the barren planet. But Sallman and his team were not the first to make contact. Smugglers from his own planet had begun trading with the natives for a new and virulent narcotic - the most dangerous drug in the universe. Now Sallman would have to find out how he could survive on a planet so cold that sulphur was solid and water was liquid - and how to stop the source of the deadly drug!