It is a dark time in the universe. Planet after planet is falling to an unholy army of Necromongers - conquering warriors who offer ravaged worlds a simple choice: convert or die.

Those who refuse their rule hope in vain for someone or something that will slow the spread of Necromongers. But rebels are short-lived and saviours, it seems, are in short supply.

When things get bad, weary survivors turn to myths for comfort - murmured prophecies, vain hopes, legends of good vanquishing evil. But good isn't always the antidote to evil and legends can be wrong. Sometimes the only way to stop evil is not with good - but with another kind of evil.

So an unlikely figure is summoned from exile and asked to join the fight: Riddick (Vin Diesel), who couldn't care less who's in charge of the universe, just as long as he's left alone. Since leaving a god-forgotten planet in the Taurus system five years ago, the wanted fugitive hasn't looked back.

Most of his time has been spent evading capture and ghosting whatever mercenaries are on his tail. To him, it's all the same, apocalypse or not - this one-man army is interested only in saving his own life. Get in his way and he'll gladly take yours.

But something has been set in motion, and the coming confrontation propels Riddick into a series of epic, winner-take-all battles: from an idyllic, multi-cultural civilisation under siege; to a subterranean prison carved out beneath the surface of a hellish, volcanic planet; and finally, aboard the massive, baroque Necro mothership and the seat of power in their black empire - the Basilica.

Featuring an ensemble cast under writer/director David Twohy, the science fiction action-adventure epic The Chronicles of Riddick continues and expands the story of cult anti-hero Riddick, with Vin Diesel reprising his star-making role from Twohy's cult hit Pitch Black.

With Pitch Black, Twohy and Diesel created an anti-hero in Riddick, whom the actor calls "a seemingly nefarious character who ends up being your only hope."

Riddick is the antithesis of the staunchly upright movie hero. According to Diesel: "Riddick, who has been counted out, given up on, overlooked and misrepresented, winds up being the one you are praying succeeds in saving you and everyone else in the universe."

"We actually started to think about a second Riddick movie when we were in post-production on Pitch Black," recalls Twohy. "And I knew the trap that other sequels had fallen into, replaying the same thing over and over again. I said that the key to a sequel is not to do the expected. Don't go back to the same planet, don't meet the same creatures and don't even let it be a creature movie. We actually changed genres from horror to science fiction action-adventure. We wanted a metamorphosis rather than a re-run."

To attract Judi Dench to the role of Arereon, Diesel flew to London to watch her perform onstage, and filled her dressing room with flowers.

She agreed to read the The Chronicles of Riddick script and was "terribly flattered that somebody of Vin's age wanted me to be in his picture."

She had, of course, already scored some street credibility' as James Bond's boss, M, in the most recent 007 films of the series, but Dench freely admits: "I've never done a film like this and never one of this magnificent scale."

Like most actors who play villains, Colm Feore had to find a point of empathy with Lord Marshal, leader of the race whose overriding goal is to cleanse the universe of all human life.

"I don't see him as an evil man," he says matter-of-factly. "He's a warrior priest. He's called Lord Marshal,' but I see him very much like Julius Caesar - a Roman emperor, conquering barbarian lands and bringing under his empire whatever new worlds they come into contact with.

"In that vein, he looks at Riddick as a man with enormous potential."

Thandie Newton was cast as the purely evil Dame Vaako. The actress, who says she tends to play "characters you sympathise with," loved Dame Vaako's "unashamed" lust for power.

"It was very different from anything I've ever played before, and I really had to fill a regal pair of shoes. It's not something that comes naturally to me, to have that kind of poise, stature and authority."