Season 10 episode 15 of CW's "Supernatural" will deal with Sam (Jared Padalecki) going behind Dean's (Jensen Ackles) back to find a cure for the "Mark of Caine". "The Things They Carried" to be aired on 18 March (Wednesday) will also bring the Winchester brothers a new supernatural element to kill: Khan worm. 

In season 10 episode 14, Dean had decided that he will abandon the pursuit for a cure for the "Mark of Caine". However, his younger brother, who had admitted to their angel friend Castiel (Misha Collins) towards the end of the last episode that he believes Dean is in trouble, is still researching to find a cure. With the "Mark of Caine" still overpowering Dean, Sam's life is also in danger, according to Caine's (Timothy Omundson) prediction in "The Executioner's Song".

The "Mark of Caine" is the source of the First Blade's power, which is the only known weapon that can kill the knights of hell - a unique breed of demons created by Lucifer and Caine. The mark was transferred to Dean by Cain himself, so that the hunter could kill Abaddon, the only knight of hell remaining alive save for Caine.  

The "Mark of Caine" combined with the First Blade however, fills the owner with a murderous rage that can only be quenched by killing the opponent. And more the person kills, the hunger for blood steadily increases. The blood lust filling the person wielding the mark is clearly seen in Caine, who was living peacefully for centuries. He killed once, to save Dean and the king of hell Crowley (Mark Sheppard) from demons, and gained back the incessant need to kill. 

Caine had warned Dean of such a future and made him promise that the hunter would find and kill him in case of such an event. Sparing not even children, Caine goes on a killing spree, forcing Dean to find and kill him personally. In the spar of words that occurs before killing Caine in "The Executioner's Song", Dean and Castiel question him on how to destroy the mark. 

However, the former leader of the knights of hell tells them that there is no cure, and that he is a living proof of that. He also warns Dean that he is living Caine's life in reverse; his story started when he killed his brother Abel, while Dean's will end with him killing Sam. 

The only person who might have a clue about the cure for the "Mark of Caine" is Metatron (Curtis Armstrong), who demands a favour for every piece of information he passes on. That last time he tried to interrogate Metatron, Dean almost killed the Scribe of God. Not wanting a repeat of the incident, Dean decides to forget about looking for a cure. 

However, when an eerily-calm Dean tells Sam and Castiel that he is fine after killing Caine, the duo refuse to believe. Sam continues his search for the cure behind Dean's back. And although Dean catches a scent of it, he decides to let it go, so as to focus on a pressing case. 

Cole (Travis Aaron Wade), who tried to kill Dean in the first half of Season 10, is back for "The Things They Carried". He reveals that 'Khan Worm", the supernatural being created by Eve, Mother of All, is turning men into murderers and joins hands with the Winchester brothers to kill it. Unfortunately the worm infects Cole; it is not known whether he will survive of if the Winchesters will have to kill him.

While Crowley and his mother Rowena are not mentioned in the synopsis for episode 15, the teaser suggested that the duo will be seen again. Rowena has been manipulating Crowley since she returned, turning him against the Winchesters and even convincing him that his loyal second-in-command was plotting against him. 

Supernatural will return in a new time-slot, as the CW series will now air every Wednesday at 9.00 pm starting 18 March.