Them (2007)

The activities of a sleeper cell from another world operating in modern-day Los Angeles. The agents arrive emotionless, follow orders without question, and none of them knows the true nature of their mission on Earth. What a few of them do know, however, is that something unexpected has happened: Our emotions affect them like a dangerous, uncontrollable virus. Once indulged, any feelings they have toward us can suddenly shatter their carefully codified order.