BOOM! Nuclear bomb in downtown Houston.

HoustonChronicle.com - Computer model maps out impact from attack on city

The nuclear bomb is small enough to be hidden in a briefcase, but its force levels downtown Houston, flattening most of the 58 skyscrapers and killing about 130,000 workers.

Stunned and injured, those who can walk among the approximately 15,000 survivors downtown stagger away from ground zero covered with invisible and deadly particles of radiation and dust from crumbled buildings.

The bomb explodes outside City Hall, destroying that building, the Houston Police Department's headquarters and the Harris County administrative offices. It kills most local leaders and law enforcement officials, crippling the city's immediate ability to respond to the disaster.

The wind drags the deadly radioactive cloud through the East End and beyond the Loop, killing 10 percent of those in its stream and sickening thousands more.

The chaos and devastation eclipses the Sept. 11 attacks on the World Trade Center.

One of three terrorist attack scenarios modeled for Houston.