According to the Wiki article on V:
The world awakens to find spaceships hovering over all major cities. Though the aliens claim to come in peace, some do not believe them. Homeland Security agent Erica Evans discovers that the aliens have plans to infiltrate our governments and businesses in a plot to take over the planet. Erica joins the resistance movement, which includes Ryan, an alien who wants to save humanity. However, the aliens have recruited earth's youth, including Erica's son, to serve unknowingly as spies.