Heredity is dependent on the complex patterns of genes and chromosomes, which are particularly vulnerable to radiation. An error in a biological research unit led to the birth of a thing so bestial and so powerful that it became a target so Security.
As it grew, its strategic potential developed until whispers of its monstrous power filtered out to the rest of the world. Other nations were interested and one intrepid agent reached the secret bunker where the powerful thing was kept. His interference shattered a safety device and the thing escaped.
It strode across the world with the fury of a tornado. Nothing seemed able to stand in its path. Mighty cities were shattered like ant-hills as the mutant monster continued its rampage. Dazed, disorganised humanity strove desperately to strike back before it was too late...