Margo Greene is an evolutionary biologist at a Chicago museum. When a coworker's research crate arrives without the researcher, Green and her mentor, Dr. Forck, unpack and investigate the material which includes a superstitious relic and an unidentifiable virus found on some leaves native to Brazil. At the same time, police Lieutenant Vincent D'Agosta is investigating a ship full of dead people that arrived from Brazil. When murder occurs in the museum that is linked to those on the ship, D'Agosta seals off the museum. This infuriates the museum curator Ann Cuthbet who's hosting an exhibit opening gala reception that even the Mayor will be attending. D'Agosta and Green find out, however, that the killer is an ever evolving creature intent on killing everyone trapped in the museum.