The midseason premiere of the long-running The CW series "Supernatural" saw an explosive twist involving Castiel (Misha Collins), the Winchesters' best angel buddy. In the upcoming episode, viewers will see exactly how he has changed and how the brothers are going to deal with it.

Last episode, Sam (Jared Padalecki) and Dean (Jensen Ackles) both thought that Lucifer (Mark Pellegrino) was gone, thanks to Rowena's (Ruth Connell) witch work. Crowley (Mark Sheppard) conspired with the brothers and forced his mother to put the devil back in the hole. It looked like they succeeded, but when they eventually got out of the cage, Castiel was acting weird. It turned out he agreed to be Lucifer's meat suit to defeat Amara (Emily Swallow).

Castiel believed that Lucifer could match the Darkness with his powers. Prior to that, he tried to take down Amara using his angel sword, but as he witnessed, even God's thunder barely hurt her. Sam and Dean, although brave and valiant, were just humans and of no match to the awesome powers of God's sister. That was why, when Sam refused Lucifer's proposal that they fight her together, with the former being used as a vessel, he made the risky decision.

In actuality, Castiel was brought to Hell by Amara to warn Lucifer that she was coming. Dean, on the other hand, was there to save his brother. The angel did not know of Dean's plans to put Lucifer back in the hole. During the scuffle that followed inside the case, Lucifer was winning. But when he was about to kill Castiel, he vanished. Rowena's spell worked, or so they thought. Now that Lucifer is out and possessing Castiel's human body, viewers can expect the Winchesters having a difficult time dealing with him.

Also in episode 11 titled "Into the Mystic," CarterMatt reports that the Winchesters will probe into the mysterious death of people seconds after hearing a specific song. What kind of creature are they going to face next?

"Supernatural" season 11 airs Wednesdays at 9 p.m. EST on The CW.