Five years after surviving a horrific night with those flying bat-scorpion things, Riddick (Diesel) is on the run from a tenacious mercenary (Chinlund) trying to claim a large reward. His latest escape takes him to the peaceful multi-cultural planet Helion (home of the other Pitch Black survivor David), which is currently being invaded by the Necromongers, galactic crusaders who demand you convert to their "underverse" religion or die. To save Helion--and the galaxy--Riddick must learn more about who he is, fulfil a prophecy, and escape from the underground prison on the molten-lava planet Crematoria.

Yeah, OK. There's a lot of plot and silly names for people and places, but that's not the problem; the film fails because the complex chaos masks an underlying stupidity. Twohy and Diesel take this all so seriously that it's impossible to enjoy. The dialog is grunted spasmodically, the characters are all moody rebels, the stunts defy any sense of reason and everything is so overwrought that we just give up.

That said, the cast is quite good in a laughably pretentious way. Diesel is always fun to watch, although the word "fun" seems to be missing from his vocabulary at the moment. And what the rest of these fine actors are doing in this overexcited action movie is anyone's guess: Dench's whispy Elemental provides fatalistic pronouncements, Feore's frenetic leader ("a holy half-dead who has seen the underverse!") is just power-mad, Newton's femme fatale vamps it up, Urban's brooding warrior simmers with dark ambition, Roache's high priest offers one small surprise, and so on.

What's left amid the cacophony of incomprehensible battles and stunt sequences is a chance to giggle at the silly names, unintentionally hilarious lines of dialog, and camp sets and costumes. Let's face it: With all the vicious violence, we need a whiff of honest wit. Without it, the film is as corny, bombastic and soul-destroying as the Necromongers themselves.