A terrestial dust cloud had lowered the temperature of the sun's rays enough to bring on the second Ice Age and the world population had moved underground as city states burrowed in layers under the ice. Generations later, in 23,000 A.D., 17-year-old Jim Barnes, his father and colleagues were arrested for high treason. Only one rime in sub-ice New York city state was more serious than breach of the population control (each family is limited to one child) and that is to attempt contact with another city state. Jim's father and his friends had discovered that the temperature was rising-- the ice is going to start rolling back. In attempting to check their findings with another part of the world, they reach London by radio. Fear of change, fear of the unknown, distrust of a sky they've never seen, drives the senile city council to exile the group. A plug is bored out of the ice, and Jim along with a fully equipped party is set out into daylight to survive a trek across the frozen Atlantic to an equally fearful London by solar-powered sledge. Food, the weather and some abominable Ice Age men, who never went under, keep it a properly chilly story about the unification of a thawing world. You might call it an easy reader in science fiction. It has no invented planets, creatures or special language-- just an invented situation with possibilities that the dialogue doesn't consistently live up to, but that's just a small rough patch in the ice.