The Winchester brothers have long been looking for the cure that would rid Dean of the Mark of Cain. And just when that long-lost treatment is found, something twisted plots to take it away from them. 

In the new episode of "Supernatural" very aptly titled "Book of the Damned," Charlie informs Dean and Sam that she has finally located the Book of the Dead, which will help free Dean from the Mark of Cain before its undesirable and evil effects do any more damage. However, there is no promise of their success as Jacob Styne declares that the book belongs to his family and even shoots Charlie. Ultimately, he assures all three that he will do everything in his power to have the Book of the Dead. 

If actor Jared Padalecki's words are something to go by, it looks like Sam and Dean' struggle to get the cure will not be ending anytime soon. Worse, it may take a darker turn for his character, Sam. 

"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," Padalecki said during the recent Supernatural Seattle Con. 

"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," he then teased. 

On the other hand, Castiel and Metatron have something to search for as well. The two team up to find the former's grace but their journey entails "a couple of road bumps" and this makes the task harder than it already is for both of them.

Episode 18 of "Supernatural" season 10 "Book of the Damned" will air on April 15.