A retriever who specializes in obtaining rare goods comes after the Omnitrix. He manages to get the Omnitrix and part of Ben. Ben is sent elsewhere fighting to survive, while his friends try to figure a way to bring Ben back.
An alien race asks the team to deliver the Tiffin to another race as a peace offering. The Omnitrix changes Ben into a new form, that's highly aggressive which causes other problems on their peace mission.