Now that "Supernatural" is inching towards its final episode of season 10, devout viewers should expect the plot to revolve around Dean's Mark of Cain curse. Cain revealed that his protégée, Dean, is living his life in reverse. Hence, the only way he can "cure" himself is by murdering his brother Sam since Cain's curse was triggered by the death of his brother, Abel.

According to TVGudie's official episode synopsis, Charlie resurfaces and calls the Winchester brothers to tell them that she has found the Book of the Dead which could possibly help remove the Mark of Cain curse from Dean. However, things take a turn for the worse when she tells them she has been shot by a man named Jacob Styne, as per Hollywood Hills' synopsis. This unknown man claims that the book belongs to his family and he won't rest till he has it. The Winchester brothers race to find the book before Styne can get his hands on it. But will the duo be able to get their hands on the book before Dean kills Sam?

Meanwhile, Castiel takes a trip to Metatron to find the angel's grace but the ride isn't exactly smooth sailing. While many have seen Dean go dark this season, will Sam go too?

At Seattle's salute to Supernatural, star Jared Padalecki told the audience that viewers will see Sam's darker side this season. He said, "Sam does have a lot of darkness in him, so does Dean. I think it's one of the themes that, as long as Supernatural is alive, that theme is going to be around. Both of these guys are struggling with their demons, struggling with their past. I think we will see Sam get dark. I know we do a little bit this season that you haven't seen yet. So I think you'll see it from Sam and Dean both."

"Supernatural" airs on Wednesday, April 15 at 9 p.m. ET on CW.