Allowing Ultimate Kevin to absorb some of Gwen's power gives him a taste for more, enabling Gwen to be used as bait. She and Ben and a few unexpected others work in tandem to delay Kevin long enough for Cooper and Darkstar to fashion a solution from a surviving fragment of the Dominus Librium. As fighting intensifies, though, it's hoped the proposed cure can be ready before anyone dies or before there's no choice but have Kevin put down.
Did You Know?
This is the only episode in the Ben 10 franchise in which Kevin's step-father, Harvey Hackett, appears. See more
[emerging from the trunk after Kevin's destroyed the other clones
Luckily, I always keep a spare in the trunk. That should be enough of a head start.