In the early twenty-first century Earth is visited by an alien race, the Taelons. They claim they wish to share knowledge with the rest of humanity in the hopes of getting to know us better. William Boone is assigned protector of Da'an, the Taelon "companion" for North America. But Boone is really working for the human resistance who are trying to learn the Taelons' true motives, which may not be as generous as they claim. At the end of the first season Boone was killed by the taelons. His character was replaced by Liam Kincaid. An alien hybrid taking on the persona of a former comrad of Boone's. We learn in Season 2 that the taelons are at war with another alien race, the Jaridians, and that earth has a key role in this conflict. He joined in Season Three with another double agent Renee Palmer. As season four drew to a close, the Taelons and the Jaridians were on the verge of extinction. Ironically, their last chance for survival was to join with one another. This joining caused the Atavus to be unleashed upon the earth bringing about the final conflict. Renee becomes a fierce crusader on a mission to expose and destroy the Atavus before they take over the world.
By the end of the series the Atavus are returned to their homeworld setting right the ancient wrong of the Atavus leaving their home
"They are the Companions. Aliens, come to earth on a mission of peace. Their true mission, the secrets they hide, forever alter humanity. In the struggle for our planet, the battle between these Taelon Companions and the Human Resistance, holds the key to Earths future and the fate of mankind. On EARTH: Final Conflict"