Mutant snakes survived a terrorist attack on a government laboratory, and they now threaten the town of Santa Mira Springs, California. Seismic activity has brought snakes to the surface, where residents are being bitten. Victims can transmit the virus to healthy persons. The military puts the town under quarantine. Local physicians try to control the epidemic, while the military is primarily concerned with keeping the virus a secret.
Trapped in their New York brownstone's panic room, a hidden chamber built as a sanctuary in the event of break-ins, newly divorced Meg Altman and her young daughter Sarah play a deadly game of cat-and-mouse with three intruders - Burnham, Raoul and Junior - during a brutal home invasion.
Kay and Jay reunite to provide our best, last and only line of defense against a sinister seductress who levels the toughest challenge yet to the MIBs untarnished mission statement: protecting the earth from the scum of the universe.