Ben 10: Alien Force is the sequel to the Ben 10. The series takes place five years later after the original. Ben no longer wears the Omnitrix, and his cousin, Gwen, has honed her skills in magic. But when an alien invasion of the DNAliens strike Earth and Grandpa Max goes missing, Ben decides that it's hero time once again. He's not alone, as he is joined by Gwen, and even his old archenemy, Kevin Levin. Now it's time once again for Ben to begin his quest to find his grandfather and stop the invasion from the evil DNAliens. Our heroes will cruise around with Kevin and his car. The show tackles some mature issues, although the target audience is the same.
Despite being warned by Paradox, Gwen travels back in time to prevent the accident that turned Kevin into a monster from ever happening. Gwen returns to the present only to find that her time traveling caused a series of events that led to Hex ruling the world. It's up to her to fix the future that she created.
In the middle of fighting another Techadon robot, Ben, Gwen, and Kevin are unexpectedly transported by the Omnitrix to an alien planet called Primus. They soon discover that they are not alone and that Vilgax is there to stop the Omnitrix from its source.
Zaw-Veenull, a Luoadan Ambassador asks Ben to deliver their Crown Prince, Tiffin, to Jarret in order to keep peace between the two species. Shortly after their trek begins in space, the Omnitrix malfunctions and turns Ben into an Appoplexian named Rath who wants to fight anything that breathes. Rath keeps picking a fight across the galaxy with anyone who crosses their paths and things don't look good as they approach the Phontopage homeworld on a mission of peace.
Ben, Gwen, and Kevin finds a curious alien box in an alley that has the ability to turn into a robot version of whatever it sees. This spells trouble for our heroes when the Vreedle Brothers shows up and try to take it by force. The robot becomes very dangerous and Ben must stop the Vreedle Brothers from capturing the device while also trying to keep the device from blowing up downtown Bellwood!
Kevin and Darkstar find a mysterious Artifact that could return them to their previous forms, but do not consider the consequences.