When a train's passengers are exposed to a deadly virus, it triggers an international incident.

After a beaker carrying a deadly virus is shattered during a terrorist attack on the Geneva's International Health Organization offices, one of the terrorists escapes onto a transcontinental passenger train. As the military diverts the train toward the Cassandra Crossing, a rickety bridge that likely won't be able to sustain the train's weight, the passengers try to cope with the spreading infection.