Charlie shows 'Book of the Damned' to Sam and Dean
Charlie shows 'Book of the Damned' to Sam and DeanScreenshot/Youtube

Season 10 Episode 18 of The CW series "Supernatural" will be aired at 9 pm (EST) on Wednesday, 15 April. With the last episode, "Inside Man", one major issue in the Winchesters' lives, Rowena (Ruth Connell), has been eliminated, leaving the hunters and their angel friend with just one task at hand -- curing Dean's (Jensen Ackles) Mark of Caine.

The promo for "Book of the Damned" shows that beloved character and token Winchester sister Charlie (Felicia Day) is back and she has found the item that can possibly help save Dean from becoming a demon. But, how can anything in "Supernatural" ever be that simple?

When Charlie brings the "Book of the Damned" to Sam (Jared Padalecki) and Dean, the elder Winchester brother says that the book is tricking them. Each page of the book is made out of pieces of skin and is filled with spells that are written in blood. Dean says that although "Mark of Caine" is mentioned in the book, the spell comes with a price: "It wants me to use it; but not for good".

Dean asks his brother to destroy the book, before he does something awful, but from the promo it looks like the book is not destroyed in time. Dean is seen beating up quite a few people, including Sam.

Meanwhile, Metatron (Curtis Armstrong), whom Sam and Castiel (Misha Collins) ousted from Heaven with the help of the late Bobby (Jim Beaver), is still travelling shot-gun with the angel. Castiel also seems to be hosting a violent streak, and is seen punching Metatron when he makes a wise-ass comment.

Will the "Book of the Damned" do more harm to Dean than good? Will it turn him into a demon much earlier than anticipated?

Find out in season 10 episode 18, "Book of the Damned" of The CW series "Supernatural", at 9.00 pm (EST) on Wednesday, 15 April.