Here's the article from TV Guide Magazine...

"The season opens with some bombshells!" teases creator Eric Kripke, who already jolted viewers when he sent Dean Winchester (Jensen Ackles) to Hell in May's season finale. Season 4 opens up four months later, when Dean wakes up with no memory of his torment. "What happened to Dean in Hell and to [younger brother] Sam (Jared Padalecki) when he had to be a hunter by himself will slowly come to light," Kripke says. "It gives us a nice opportunity for an internal struggle for Dean and for the brothers to surpise each other." Katie Cassidy (Ruby) and Lauren Cohan (Bela) are both gone, but Jim Beaver and Steven Williams are back as geezer demon fighters Bobby and Rufus. Get set for a revealing flashback to the Winchester's parents' teen years, a homage to 1930s monster flicks and a bloody Halloween show!!!!!