Fifteen-year-old Daniel has followed in his parents' footsteps as the Alien Hunter, exterminating beings on The List of Alien Outlaws on Terra Firma, but when he faces his first of the top ten outlaws, the very existence Earth and another planet are at stake.

As Daniel X continues to hunt for intergalactic aliens, he and his friends go to England searching for Beta, an outlaw who takes the form of fire and who killed Daniel's parents when he was two years old.

Daniel faces dastardly Number Two, who has slowly been amassing an underground army of aliens to help him enslave Earth's population in preparation for the arrival of Number One, the most powerful alien in the universe and Daniel's arch-nemesis.