It takes a few minutes to get the mind and the eyes around the fact that, yes, that's the great Brit-thespian Michael Sheen, impersonator of Tony Blair ("The Deal," "The Queen") and David Frost ("Frost/Nixon"), transforming into a werewolf in "Underworld: Rise of the Lycans." But it is Sheen, all buff and hairy and toothy, giving his all in a struggle with vampire Bill Nighy over the vamp's fanged daughter, played by Rhona Mitra. That cast makes this prequel to the movies that showed the world how good Kate Beckinsale looks in leather worth watching.

"Underworld," a tale of the feud between werewolves and vampires and their immortal daylight-hours protectors, "Lycans," morphs into a "Spartacus" with fangs in the third film. The vampires and their leader have enslaved the first Lycans, keeping them from transforming into werewolves with these magical lock-collars. And Lucian, "the first Lycan" (Sheen), a lowly blacksmith kept around to kill "your own kind" (werewolves), must lead the other Lycans to freedom.

Lucien is an inspiring leader and a dynamic speaker, as you'd expect from the onetime talk-show host and former head of Britain's Labour Party.

"You have a choice," he bellows, "freedom, instead of pestilence" and slavery. This Braveheart wants to drive a stake through the heart of their masters.

But the cadaverous Viktor (Nighy, reprising his role from the first two "Underworlds") is cunning. He's not about to let his slaves revolt, even if Lucian is "a credit to your race."

The "pestilence" has to do with how these creatures were born — a virus that made the original "immortal," Corvinus. He's referenced in the film (Derek Jacobi played him in the original "Underworld") and there are other efforts to tie the film into the "Underworld" continuum, including a cameo in the finale. That virus is what is passed on by biting.

The effects-designer-turned-director of Lycans has shot a dark-on-dark film, with most of the action cast in the shadows — assaults by waves of digital werewolves, dungeons, the blue-black castle keep where the vampires rule the roost. The sword fights (vampires need weapons to dispatch werewolves) are properly bloody and cut in a seizure-inducing blur.

The film would all be a complete bore if it weren't for the odd sparks of wit, and the sparks set off by Sheen and B-picture queen Mitra. Vampires and werewolves could teach India a little something for the Kama sutra.

But they've finished their trilogy and explained (sort of) the origins of this fictional universe. Now that there's enough vampire-Lycan bloodletting for a boxed set, perhaps they'll put these dogs (and bats) to rest.