The novel explores the sudden and catastrophic onset of the next glacial period, a topic of serious scientific discussion in the 1970s. The plot is driven by the warnings of a climatologist, Dr. William Stovin, whose predictions of rapid global cooling are largely ignored by the U.S. National Science Council until it is too late.

As the new Ice Age begins unexpectedly, major northern cities like Chicago, Oslo, Montreal, Moscow, and Leningrad come under siege by extreme cold and are forced to evacuate. The book details the collapse of normal life and the desperate struggle for survival as technology and governments prove inadequate to handle the rapid climate catastrophe.