From the back cover:
For years, a shadow war has raged against the Universal Brotherhood and its savage masters parasitic insect spirits that feed on human hosts. Now Chicago has become the final battleground in the war against the bugs. Overrun by the horrible predators, the city has been quarantined by the UCAS military leaving its inhabitants to fend for themselves while 'other solutions' are considered. Hundreds of thousands remain trapped within the walled Containment Zone, at war with brutal gangs and ruthless warlords that rage unchecked and the unnatural menace threatens them all.
BUG CITY is a SHADOWRUN sourcebook that picks up where the novel BURNING BRIGHT left off. It provides a detailed description of life in the Containment Zone and includes game information on the changes in Chicago's physical and magical nature, profiles of the city's important residents, and expanded rules for the city's terrible ravagers - the Insect spirts themselves.