 Grandpa Simpson reveals to Bart that he and Montgomery Burns were part of a World War 2 unit known as the Flying Hellfish, which stole priceless art from a German castle during the war, of which the last surviving member would inherit the fortune. When another member of his platoon dies, Abe and Burns remain the last two survivors, and Burns vows to make sure Grandpa doesn t become the last Hellfish, until Abe and Bart vow to find the fortune before Burns does.