Cinema Science

This is from online script review of M. Night Shyamalan's next film, The Happening. It is the first plot description I have read of it anywhere.

Reports of strange deaths begin to come in from cities around the world. It's only after the main characters -- Mark Wahlberg, Zooey Deschanel -- begin their trek out of Philadelphia do they begin to realize the scope of the death toll. People everywhere are succumbing to an urge to kill themselves. [It soon becomes clear] that the deaths have been caused by the release of a toxin by surrounding plant life in an evolutionary last-ditch attempt to protect themselves from the predator that endangers them the most.