A retriever who specializes in obtaining rare goods comes after the Omnitrix, dimensionally separating the Omnitrix and a part of Ben. Ben is sent elsewhere, fighting to survive, while his friends try to figure a way to bring him back.
Sunder, a retriever of rare objects, comes to collect the Omnitrix but winds up sending Ben to the Null Void dimension without the Omnitrix or his left hand. As the separated hand fights to avoid Sunder's capture while seeking Julie, Gwen and Kevin for help, Ben fights for his life against ravenous monsters, "single-handedly."—statmanjeff