"Supernatural" season 9, episode 20 airs tomorrow night - find out where to watch "Bloodlines" online via a free live stream of the CW. "Supernatural" season 9, episode 20 will be a backdoor pilot for the spin off series of "Supernatural," titled "Bloodlines."

If you can't make it to a TV by 9pm EST tomorrow night to catch "Supernatural" season 9, episode 20, click here or here to watch "Bloodlines" 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: "SAM AND DEAN INVESTIGATE MONSTER FAMILIES IN CHICAGO - Sam (Jared Padalecki) and Dean (Jensen Ackles) investigate a case in Chicago, where they discover that various mafia-esque monster families are, unknown to humans, running the underbelly of Chicago. One is a family of shapeshifters run by Margo Lassiter (guest stars Danielle Savre), whose leadership is thrown into question when her brother David (guest star Nathaniel Buzolic) returns home. The other reigning family in town is made up of werewolves, lead by Julian Duval (guest star Sean Faris). While in Chicago, Sam and Dean meet Ennis (guest star Lucien Laviscount), a man with a personal vendetta against the monsters. The Winchesters warn Ennis about heading into the hunter lifestyle, but Ennis refuses to listen and starts down a dangerous path. Robert Singer directed the episode written by Andrew Dabb (#920)."

Tomorrow night's episode will be a backdoor pilot for the spin off series of "Supernatural," titled "Bloodlines." According to ScreenCrush: "'Bloodlines' focuses on Ennis Roth (Lucien Laviscount), who puts his police academy training to use as a monster hunter after his fiancée is killed in the crossfire of the monster war dominating Chicago. Elsewhere, Melissa Roxburgh plays leading lady Violet Durant in the backdoor spinoff pilot, a member of the powerful werewolf pack who hides her true nature because of her forbidden love for family rival David ('The Vampire Diaries' alum Nathan Buzulic).

"Also cast in 'Supernatural: Bloodlines' is Danielle Savre as Margo, the acting head of the shapeshifter Hayden family, an ex-punk rocker-turned-corporate professional who feels threatened only by the return of her brother David. Stephen Martines will play Detective Freddie Costa, a world-weary Chicago cop who acts as a mentor to leading man Ennis, but is also on the payroll of one of the powerful monster families. Finally, 'Pretty Little Liars' star Sean Faris will take the role of Julian Durant, the "savagely handsome, strong, arrogant" twenty-something brother of Violet, and nemesis to Ennis."

"Supernatural" season 9, episode 20 airs tomorrow night, Tuesday, April 29 at 9:00 PM EST on the CW.