The plot in your average martial arts flick is never more than an a thin excuse to get the hero mad enough to kick ass. But I've never come across one as exotically ludicrous as ''You killed my father and stole my elephant!'' That's what sends Cam (Tony Jaa) from his native Thailand, where he raised sacred pachyderms, to Australia, to settle the score. It's silly, at times laughable, sure, but Jaa has a reckless, bone-cracking grace that transcends the film's triviality. For fight fans, he's worth the price of admission.