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Sergei Bachlakov, The CW
Sam (Jared Padalecki) confronts demon girl Ruby (Katie Cassidy) on The CW's series "Supernatural."

There aren't many shows that could largely reinvent themselves in their third seasons and come out on top. That would require almost, ahem, "Supernatural" intervention.

And yet The CW's Thursday-night (8 p.m., Ch. 30) action/horror/thriller/comedy has done just that. It's better than ever.

For those of you who haven't checked the series out, "Supernatural" began as the story of brothers Sam (Jared Padalecki) and Dean Winchester (Jensen Ackles), whose mother was killed by a demon when they were very young. Their father, John (Jeffrey Dean Morgan), seeking revenge, became a skilled demon hunter and raised his sons to follow in his footsteps.

When the series debuted in the fall of 2005, the elder Winchester was missing and his sons were looking for him, battling various demons and legends out of folktales along the way.

Much to their credit, creator/executive producer Eric Kripke and his team didn't let that drag on forever. In the two-parter that aired as the Season 2 finale back in May, the Winchesters hunted down and killed the Yellow-Eyed Demon who started all of this.

John, who had traded his life for Dean's earlier in the season, returned in ghostly form to wrap up his story line as well. But while this marked a major turning point for "Supernatural," it didn't by any means leave the series with nowhere to go.

Before the Yellow-Eyed Demon could be destroyed, he opened a gate to hell (in Wyoming, of all places) and unleashed scores of demons who are now free to pursue their evil ways on Earth. So Sam and Dean set out to hunt them down and send them back to hell.

Not only that, but Sam was actually killed at the end of last season, so Dean made a deal with a demon that gave Sam back his life — but at the cost of his own. Dean has one year to live, then he's headed for hell, too.

So the boys are hunting demons, and Sam is determined to find a way to void the deal and save Dean.

Don't let the fact that there's a lot of history behind "Supernatural" scare you away. If there were some kind of award for best opening synopsis by a prime-time series, this show would win hands down.

In the space of a minute or so, each episode opens with a series of flashbacks that establish the show's mythology all the way back to the beginning so you can tune in at any time and catch up. Heck, if there's something from a specific episode in the show's past that applies to the current episode, that's in there, too.

The continuing story lines are a backdrop to individual episodes that remain as exciting/creepy/funny as ever. So far this season we've seen demons that represent the seven deadly sins; a cursed rabbit foot; changelings; a town overcome with vice; murderous fairy tales; the ghost of a cursed seaman; and vampires.

As deadly serious as this can be, the one about the cursed rabbit foot was hilarious.

This Thursday it's a Christmas episode, complete with a very unmerry Anti-Claus.

My only complaint would be that the show seems a bit grosser this season. We're seeing more of the gore than before — but still far less than we see in so many of today's horror flicks.

"Supernatural" has added a pair of recurring female characters who are very different, but both have worked out great. Ruby (Katie Cassidy), a mysterious blonde, knew something the Winchester brothers did not about their past and Sam's possible future — that he was supposed to lead the Yellow-Eyed Demon's army of demons that would overun the Earth.

Turns out she's a demon herself, but she's not like other demons. And we're still waiting to find out what her motives are.

Bela (Lauren Cohan) is a fellow demon hunter, but she's not exactly altruistic. She retrieves supernatural artifacts for wealthy buyers. With Bela, it's all about profit. And when she crosses paths with the Winchesters, things get rough.

She did, after all, shoot Sam in one episode. But she only winged him.

As for Bela and Dean, they've got chemistry. But he isn't sure whether he wants to kiss her or kill her.

One thing that is certain, however, is that "Supernatural" has done what shows like "The X-Files" never could manage. It tied up the loose ends from its original premise in a way that was hugely satisfying for viewers without pulling the pilings out from under the show's mythology. And as it heads for its 52nd episode on Thursday, a show that has been good from the beginning is still getting better.

E-mail: pierce@desnews.com