In New York City's Central Park, people begin dying by mass suicide. Initially believed to be caused by a bio-terrorist attack using an airborne neurotoxin, the behavior quickly spreads across the northeastern United States. High school science teacher Elliot Moore and his wife Alma are convinced by Elliot's mathematician colleague Julian to accompany him and his daughter Jess on a train out of Philadelphia. During the trip, the group learns that Boston and Philadelphia have also been affected. The train loses all radio contact and stops at a small town. When Julian learns that his wife has left Boston for Princeton, he decides to go look for her, and entrusts Jess to the Moores. However, Princeton is affected by the time of Julian's arrival, and he dies by suicide.