Supernatural season 10 goes on a week's hiatus and will return with an all new episode on 15 April.
Episode 18 is titled Book of the Damned, where Felicia Day will return as Charlie.
The official synopsis reads: "Charlie (guest star Felicia Day) calls Sam (Jared Padalecki) and Dean (Jensen Ackles) to tell them she found the Book of the Dead which could help remove the Mark of Cain. The Winchesters race to her after she tells them she's been shot by a man named Jacob Styne (guest star Jeff Branson) who says the book belongs to his family and he won't rest until he gets it back."
Episode 18 will also address the problem of Castiel's stolen grace.
According to the synopsis Castiel (Misha Collins) will take a trip with Metatron (guest star Curtis Armstrong) to find the angel's grace but "they hit a couple of road bumps along the way".
Jared Padalecki who plays the younger Winchester has teased that Sam might go dark in the season 10 final episodes.
"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," Padalecki explained at Seattle's Salute to Supernatural.
"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."
"We are filming the final arc of season 10 right now and it's one of those really intense final arcs, I mean it's probably the most intense I can remember since like season five or something like that," Padalecki said about the season 10 finale.
Supernatural airs on Wednesdays at 9pm on The CW.