"Supernatural" season 9 finale airs tomorrow night - find out where to watch "Do You Believe in Miracles" online via a free live stream of the CW.  According to Jared Padalecki, who plays Sam Winchester in "Supernatural," the finale will introduce a new plot development for season 10, which will have a "long-lasting" effect on the Winchester brothers.

If you can't make it to a TV by 9pm EST tomorrow night to catch the "Supernatural" season 9 finale click here or here to watch "Do You Believe in Miracles" online via a free live stream of the CW.

If that doesn't work, the CW also offers episodes on their website to watch online after an episode airs.

The official synopsis for this week's episode reads: "THE SHOCKING SEASON FINALE - Dean (Jensen Ackles) feels the effects of the First Blade, and Metatron (guest star Curtis Armstrong) makes his move against humanity. Meanwhile, Sam (Jared Padalecki), Dean and Castiel (Misha Collins) face shocking consequences when taking the fight to Metatron (guest star Curtis Armstrong). Thomas J. Wright directed the episode written by Jeremy Carver (#923)."

Padalecki revealed to TV Fanatic that he was "shocked" when he read the script, as well as "absolutely excited," Fashion & Style reports.

"It wraps up the season so perfectly," Jared said, "but it also sets up, in my opinion, not just season 10, but if they want to go further it sets up a whole storyline that you can do whatever you want to with, you could go years with this storyline."

Padalecki added, "This is something that's going to have a long-lasting effect on the brothers, on the storyline, on the mythology in general."

Jenson Ackles, who plays his brother Dean Winchester in "Supernatural," told Entertainment Weekly, "It's been a tough season for me. I don't usually have to play Dean this dark for this long. Usually it's an episode, and then he comes back and is happy-go-lucky and a Dean we all love to hate or love to love, whatever side of the fence you're on."

He also mentioned viewers should be ready to cry, "considering [Padalecki's] tears were all over [his] shoulder."

Misha Collins, who plays Castiel, teased that the "Supernatural" season 9 finale will end with a cliffhanger.

"It's been a great storyline and there's more of it to play out in season 10," he told IGN. "But the cliffhanger, I can tell you, going from season 9 into season 10 is fantastic. It's great."

"Supernatural" season 9 finale airs tomorrow night, Tuesday, May 20 at 9:00 PM EST on the CW.