It should have been a moment of pure joy for Angelina Jolie. But on March 19, as she prepared to fly her newly adopted son, Pax, home from Vietnam, she received terrifying news: Her security team had learned of a plot to kidnap the 3-year-old once he and his famous mom returned to the United States.

An insider close to Brad Pitt and Angelina's security team tells Life & Style that the plot was credible and meticulously planned by a deadly ...