Sean McCarthy wakes up from a haunting dream to discover a mysterious pair of doctors in his apartment. They tell him that an aerosol device planted by terrorists infected him with a deadly virus while he was taking the New York City subway system to see a play starring his girlfriend, Megan. They do not believe that Sean will live very much longer. As they treat him nonetheless, Sean loses consciousness and drifts between reality and the dream-like memories of his last encounter with Megan, their conversations mixing with the words he overhears from the doctors. When a security guard accidentally informs Sean that the disease is spreading in the general populace, he decides to break out and make sure Megan is unharmed. But the virus may have weakened him too much to be able to make his escape.