The Event

Near the end of World War II, an aircraft of undetermined origin crashed in the Brooks Range of northern Alaska. It carried passengers who appeared outwardly human but are not of terrestrial origin. They have some genetic differences and age much more slowly than humans. Most of the survivors were captured by the U.S. government and held in a secret facility nearby run by intelligence agencies, since they have refused to disclose much about their origin. The remaining survivors, who only sustained minor injuries, were able to escape the crash scene and currently live among the population.
President Elias Martinez learns of the facility's existence shortly after his inauguration and decides, after meeting the leader of the detainees, to release them and disclose their existence to the world over the objections of the intelligence agencies. His plans are put on hold when an assassination attempt on him is foiled by means beyond human technology. The CIA, realizing that this means there are other aliens, secretly plans to find and kill them. The agent chosen to head the effort is himself an alien and that fact is unknown to the agency. The aliens are divided internally on how to respond to this.
Caught in the middle of these events is Sean Walker, whose plans to propose to his girlfriend Leila on a Caribbean cruise are cut short when she mysteriously disappears from the ship. His investigation eventually leads him to uncover the assassination plot.