may kill Sam because the grace is keeping him from reverting to his deathly state prior his possession. However, Castiel refuses to risk Sam's life. As a result, the amount of grace they gather is insufficient to track Gadreel. Sam runs into Dean on the same case in "Sharp Teeth". Although Dean tries to divert Sam from the case so that they won't have to work together again, Sam reveals that he is willing to work with Dean again so long as it is on a strictly professional basis, telling him that they cannot work on a brotherly basis anymore because Dean has lost his trust. At the end of "The Purge", Sam responds to Dean's attempts to justify his decisions by saying that Dean's choices are not as selfless as Dean paints them and that he would not have done what Dean did given the same situation, which stuns Dean into silence. The two eventually begin to come back together as Sam learns more about Abaddon's history and plans after he learns that she has been taking souls while leaving the victims 'alive', much like he was after his escape from Hell. They eventually manage to determine the location of a portal to Heaven that allows Castiel to trap Metatron while Dean kills Abaddon with the First Blade – acquired from Cain himself and the only weapon capable of killing a Knight of Hell – but Castiel is left dying of the grace he stole to regain his powers while Dean is transformed into a demon due to the First Blade's influence. Season 10 After spending six weeks tracking the transformed Dean – along with a brief confrontation with a man named Cole whose father was killed by Dean on a prior hunt – Sam manages to capture Dean while he is distracted, taking him back to the bunker to treat him with the demon cure. Despite demon-Dean's attempts to undermine his and Sam's relationship through his demonically-warped perspective, Sam is eventually able to cure Dean and restore him to humanity, although he continues to be concerned about Dean's emotional state after his time as a demon and the possibility that the Mark of Cain could transform him again. After Dean kills their ancestor Cain, Sam is weary of his brother and wants to free him of the curse. When Dean meets with Death, he offers to remove Dean