Premise

Winterland Island is the last outpost of mankind, built during the apex of a global nuclear war that took place possibly as an alternate to the Cuban Missle Crisis. In this alternate history, a group of scientists were charged with making the ultimate answer to Mutually Assured Destruction under a project named Death Blossom ... but instead constructed a device capable of housing a relatively abnormal version of a time capsule and capable of generating a force field to withstand any attack and maintain it nearly indefinately.

The story picks up decades after the Earth has been irrevocably changed into a nuclear winter with the remnants of humanity surviving under the biosphere of the force field.