The Earth passes through the tail of a comet, which dooms all human and animal life except for those who happened to be completely enclosed inside metal containers (for example, the three main protagonists spend the night in a metal shed, a steel-lined projection room, and an 18-wheeler's trailer). Unprotected people and animals quickly dehydrate and turn into piles of red calcium dust. Those only partially exposed first gradually degenerate into cannibalistic zombies for hours or days before succumbing.