HOLLYWOOD -- The joke's on anyone trying to pry clues about the next Batman flick from its brain trust.

Christian Bale, Michael Caine, director Christopher Nolan and co-writer Jonathan Nolan all collaborated on 2005's Batman Begins, teamed again for this Friday's magic-themed mystery The Prestige and will return to Gotham City for the sequel, The Dark Knight.

Yet while promoting The Prestige, none of them were revealing much about the follow-up, which due for a June 2008 release.

As previously announced, Heath Ledger will portray a more depraved incarnation of Batman's arch-nemesis The Joker.

Rumours about other villains popping up (Philip Seymour Hoffman as The Penguin? Guy Pearce as Two-Face?) remain fanboy speculation for now, as does the storyline itself.

Even Batman himself remains, appropriately enough, in the dark.

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"I have no clue what we're going to be doing," Bale says. "When I sit in the safety vault and read the script being monitored on all sides then I'll know more."

As for the unexpected casting of Ledger, who has publicly compared The Dark Knight's Joker to the psycho thugs of Stanley Kubrick's A Clockwork Orange, Christopher Nolan explains it was "just a fortunate series of events. He expressed an interested. I hadn't thought he would be interested in doing it, but I thought it would be a worth a try. It was a very early conversation. Then, you know, we realized we were seeing the same character."

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