Director Steven Spielberg (search) absolutely, positively won't reveal the plot for "Indiana Jones 4 (search)."

Spielberg, whose latest film, "War of the Worlds (search)," debuted in Tokyo on Monday, said he and "Star Wars" director George Lucas (search) are working on the movie together.

"If I did that, my really good friend and collaborator would have me on a silver platter," Spielberg told AP Radio. "I gotta be careful because if I tell you that he might take over directing 'Indy 4' himself. And I won't have a job."

Spielberg and Lucas hope to start shooting the new "Indiana Jones" movie next year with Harrison Ford (search).