Iceworld is a humorously pointed novel of clashing perspectives, which we may designate as hot versus cold. Even for readers who have not seen H. R. van Dongen's fine cover painting for the novel's first installment in Astounding, Hal Clement does not keep us long in suspense that the planet which is unaccessible because of its climate of extreme cold is our own Earth. In contrast, the dismayed observer, the alien Sallman Ken (also on the cover, not to scale!), is truly hot-blooded. Clement genially introduces mitigating circumstances: Earth, really, is not as bad as all that. Some people are even quite fond of it. Ken, of course, was prejudiced, as anyone is likely to be against a world where water is a liquid — when he has grown up breathing gaseous sulfur and, at rare intervals, drinking molten copper chloride. The mitigating circumstances are mutual, because we have two viewpoint threads alternating here, that of Sallman Ken who is evolved to live comfortably on his quite hot home-planet; Ken is a science teacher, not a scientist or expert but possessing a good general scientific knowledge. The other viewpoint is that of several members of a Terrestrial family who of course are evolved to live comfortably on our quite cold planet. The characters all are engaging, and Iceworld weaves their viewpoints, thoughts, and actions very well. The family on Earth includes young people of various ages, so this is a fine novel for teenagers as well as adults. Sallman Ken has been brought to Earth — or at least as close to it as the Iceworld’s destructive climate will allow — to solve a technical problem for a criminal syndicate of his race. They want a product found on Earth, one which is extremely valuable but so far unsynthesizable. What is it, in its natural state? How to boost their profits by getting or creating more of it? As defined, a general scientific problem, which is why the syndicate has engaged a schoolteacher with an all-around scientific knowledge. This in fact is Clement's own background and profession, so despite Ken's alienness, his character is drawn true to life. The obvious physical barrier and scientific challenge is the scarcely imaginable temperature contrast between the aliens and the world of their interest. A differently tricky difficulty is that the rather unadventurous Ken has been talked into acting as an undercover investigator for his homeworld police. Naturally, the humans on the ground have their own motivations.