The Happening (2008)

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, Julian arrives to find Princeton has been affected, and he dies by suicide.

Elliot, Alma, and Jess hitch a ride with a nurseryman and his wife. The nurseryman theorizes that plant life has developed a defense mechanism against humans consisting of an airborne toxin that stimulates neurotransmitters and causes humans to kill themselves. The group is later joined by other survivors coming from various directions, and the small crowd chooses to avoid roads and populated areas. When the larger part of the group is affected by the toxin, Elliot suggests the nurseryman was right and that the plants are targeting only large groups of people. He splits their group into smaller pockets and they walk along. The trio ends up with a pair of teenage boys, Josh and Jared, who are later killed when Elliot unsuccessfully attempts to reason with the armed residents of a barricaded house.