Used book – THE COLD WAR, Robert Silverberg, Le Livre de poche

Jim choked with anger as he looked at Colin. What a waste of effort! They had been expelled from the underground city of New York; they had had to travel thousands of miles across the surface of the glacier that had covered the world for five centuries; they had fought against half-savage men; they had eaten meat, they who had only known synthetic foods manufactured in New York's laboratories... His father, Professor Barnes, and his friends were now prisoners, and all Colin, the Englishman, could say to him was: "Excuse me, Jim, but we have orders to kill you!"