John Brunner’s 1974 Web of Everywhere is a stand-alone science fiction novel.
Skelters supplied humanity with inexpensive global teleportation1. Island paradises were but a step from vast cities. Likewise novel plagues, irate terrorists, and savage bandits were but numbers on a keypad away from vulnerable populations. Faced with a rising tide of chaos, governments lashed out with nuclear weapons. Two thirds of the human race perished.
Decades later, two men visit an outpost of the long-dead world before the Blowup.