Complete story — includes the ending
Kevin teams up with Darkstar to retrieve an artifact called Dominus Librium that could cure both of them. After getting cured, he meets Ben and Gwen, who are surprised to see him cured. Gwen gets suspicious where she learns about Darkstar's deal and arrives at his warehouse. Darkster begins to absorbs Gwen's powers, but Kevin steps in front of the Dominus Librium and grabs it in order to send all of the energy back, thus restoring Gwen's powers and turning Kevin and Darkstar back to their mutating forms. As Darkstar runs away with the destroyed Dominus Librium, Gwen, Kevin and Ben leave to have a drink at Mr. Smoothy.
Sources and content license
Source and revision history · Adapted from Wikipedia contributors, List of Ben 10: Alien Force episodes. HTML formatting and reference markers removed. · Content license