Giant spaceships appear over 29 major cities throughout the world, and Anna (Morena Baccarin), the beautiful and charismatic leader of the extra-terrestrial "Visitors", claims to come in peace. The Visitors claim to only need a small amount of Earth's resources, in exchange for which they will share their advanced technological and medical knowledge. As a small number of humans begin to doubt the sincerity of the seemingly benevolent Visitors, FBI counter-terrorism agent Erica Evans (Elizabeth Mitchell) discovers that the aliens have spent decades infiltrating human governments, businesses, and religious institutions and are now in the final stages of their plan to take over the Earth.

Source: Wikipedia.org