The Road So Far - a recap before we continue (because it's been a long while)
On the night Azazel had originally offered Mary the deal which would enable him to enter Sam's nursery years later to infect Sam with demon blood, two mysterious strangers (an older woman and an inhuman snake like humanoid) appear moments before Azazel arrives and offer Mary an alternative: if she refuses Azazel's imminent offer, they will bring John back to life once Azazel kills him – Mary accepts their terms. Azazel arrives, kills John and leaves, believing that is the end of it. The two strangers then resurrect John and leave.
John and Mary get married, have Dean and Sam, and start living the normal life Mary had hoped for.
Despite not having made the deal with Azazel, on the night Sam is six months old, Mary still is killed in Sam's nursery in the same manner (pinned to the ceiling before catching flames). John still sees something with yellow eyes leaving the room, and begins his life as a hunter, raising Sam and Dean to be hunters also.
Sam eventually rebels against the hunting life and leaves for college.
Sam goes into Law, meets & marries Jess and the two start a family. He has all but lost touch with John, and while he and Dean have the very occasional phone call, they too have mostly lost touch, having only met up once since Sam left for college (on his & Jess's wedding). Sam & Jess have their first child, a girl who they name Deanna (after Dean). Sometime later Sam is diagnosed with Leukaemia and given barely a year to live. He keeps this a secret from everyone, including Jess and Dean.
In John's world, while Sam has been studying, getting married, getting a job and starting a family, John has finally uncovered what he believes was responsible for Mary's death; a demon with yellow eyes named Azazel. He also uncovers details of what Azazel has been doing to children across the country (feeding them his blood and imbuing them with special powers in preparation for Lucifer).
Believing that Azazel killed Mary and infected Sam with demon blood, and that Sam will therefore be one of the special children, John summons Azazel in the hopes of saving Sam & purging him of the supposed demon blood. Azazel is surprised to see John, believing he killed him many years earlier, but is nonetheless unfazed. John has the Colt and threatens to kill Azazel, but the plan doesn't work. Instead, John realises he must make a deal in order to save Sam and Jess and their offspring. Azazel calls in Crowley, who is King of the Crossroads, to broker the deal between himself and John. While Crowley happily creates the contract, secretly Crowley isn't overpleased about the Apocalypse approaching as he believes things would be better left as they are.
The deal costs John his soul and he is instantly transported to hell. While John died believing that the deal saved Sam from being a special child, it only saved Sam from leukaemia, since Sam was never one of Azazel's children in the first place.
Until John summoned him however, Azazel had no idea of Sam's existence (or Johns for that matter, believing he had killed him all those decades ago when Mary refused his deal). The deal with John alerts Azazel to Sam's existence but prevents him from being able to harm Sam or his wife and children (since the deal made with John ensured their safety). Regardless of this, Sam is now firmly on the demon's radar.
John's summoning of Azazel also gave Azazel the Colt, a key component of Azazel's plan to open the Gates of Hell and free Lilith. It also gave Azazel what he believes is another crucial component for releasing Lilith; having a righteous soul in Hell (a righteous soul spilling blood in Hell will break the first Seal and release Lilith). Azazel enlists Alistair in Hell to torture and break John towards this end.
Meanwhile, Sam and Dean meet at John's funeral. Sam suspects that John may have sold his soul to save him (since he no longer has cancer) but doesn't get the chance to speak with Dean and share his suspicions, because Dean is deeply troubled/angry and leaves without giving Sam the opportunity to talk to him.
Sam & Jess have their second child, naming him Eric, in honour of John (John's middle name being Eric).
Meanwhile, Dean is hell bent on revenge for John's death, and goes on a rampage, killing every evil thing he can find. During this stint, whilst performing exorcisms, he is informed by some demons that John is being tortured in hell.
Dean tries to make a deal to save John, but no one will make him an offer. He then picks up where John left off in hunting Azazel.
Azazel is now working with Jake, the only special child to have survived following the showdown with all the other special children at Cold Oak (in the original timeline/canon Jake killed Sam at Cold Oak after which Dean sold his sold to bring Sam back).
Jake is also working with Ruby, has essentially become what Sam had been destined for in the original timeline; Lucifers vessel. On a side note, Ruby hasn't changed meat-suits and is still the original blonde version (since it had been Sam's moral objections that had made her inhabit a different body).
Dean tracks them all to Cold Oak, and then to Calvary Cemetery where they are in the process of opening the Gate to Hell. Bobby and Ellen also arrive in the hopes of helping Dean to prevent the Gate from being opened.
Jake manages to open the Gate using the Colt, but then drops it in the aftermath of demons rushing out. Dean manages to get the Colt and uses it to kill Azazel.
In the ensuing chaos, Dean goes through the Gate entering Hell without anyone noticing. Bobby and Ellen eventually manage to close the gate using the Colt (which Dean discarded after killing Azazel). Meanwhile, Jake & Ruby escape, and no one knows where Dean has gone or what he's done; no one realises he is now in Hell, having entered through the Gates in the hopes of finding & saving John.
Dean is missing for several months, no one can trace him, Bobby worries he may be dead. Then Dean finally returns to the Roadhouse. He seems different to everyone, seeming even more dark, angry and distant than he was before, and he pushes everyone away.
What no one realises is that Dean was in Hell. During this time Dean was captured and tortured. Alistair initially tortured Dean directly, but then began torturing John in front of Dean, saying he would let John go if Dean tortured souls in Hell. While initially Dean refused, he finally couldn't take watching his father being tortured, and gave in. This broke the first Seal (a righteous man spilling blood in Hell – releasing Lilith) and also freed John from the deal he & Azazel had made. John's deal having been broken meant that Sam and his family were no longer safe.
The last soul Dean tortured in hell (and the one that freed John of his deal, broke the Seal setting Lilith free and thus set the Apocalypse into motion) was that of a man. Dean tortured him to such an extent that the man became a demon, although Dean may not be aware of this.
Cas pulls Dean out from Hell soon after this and tasks him with stopping the Apocalypse since his actions in Hell have caused it to begin. He also informs him that the only way to stop it may be to accept that he is the archangel Michael's true vessel. This is the point at which Dean returns to the Roadhouse after his months long absence. He doesn't share with anyone where he's been or what has happened, but he does inform them that the Apocalypse is approaching and that he has been told this by Angels.
Dean is laser focussed on stopping the Apocalypse and is in regular contact with Angels, mainly Cas and Uriel. Michael is contacting him through his dreams, and he also suffers from severe nightmares about his time in Hell, all of which he keeps secret from everyone.
Dean reluctantly agrees to consider being Micahel's vessel, but insists on some ground rules, mainly that the angels protect Sam and his family. Dean goes as far as to have the perimeter of Sam and Jess's home warded to prevent any demons from being able to enter, and also has their (and their children's) ribs branded with protection to prevent any demon from ever being able to possess any of them. This is all without Sam's knowledge or consent. Sam doesn't know any of what Dean has done or what is going on, and Dean continues to keep his distance from Sam in the hopes of keeping Sam safe.
Because of Dean's precautions, Sam and his family are still safe despite John's deal having been broken.
The Roadhouse meanwhile is even more an operational base than before, with Bobby, Ellen, Ash and Jo all working with Dean to prevent the Seals from breaking and to prevent the Apocalypse from happening, with Dean acting as a sort of leader.
They are aware that Angels have been in touch with Dean, that Cas in particular has a close relationship with him, but Dean keeps tight-lipped about everything, although Bobby knows some details of what the Angels want with Dean.
Dean continues to be prepared mentally by Heaven (via direct communications and dreams etc) for what he is told is inevitable; i.e. becoming Michael's vessel to defeat Lucifer. As Dean is worn down, he loses hope and becomes more and more disenchanted, and more and more convinced that agreeing to be Michael's vessel may be the only way to stop Lucifer and ultimately save everyone he cares about. It is also a guaranteed suicide mission and Dean's depression and guilt about his behaviour in Hell lead him to believe he deserves this fate as a means to redemption. He continues to isolate himself and push others further and further away.
In the meantime, in Sam's life, while everything seems to be good on the surface, Sam has been burdened by the suspicion that John sold his soul to save him. Since he kept both his initial illness and the subsequent miraculous cure (and his suspicions as to the reasons for the cure, in addition to the truth about his entire hunting life) a secret from Jess, there is a slight strain in their marriage. This seems to lift when a new couple (Gavin & Stacey) and their young son move in next door. Very soon after moving in however their son dies tragically, having drowned in the swimming pool. This tragedy propels Jess to befriend Stacey and support her through this trauma, and the two couples become friends.
Over the course of this friendship, Stacey plants some ideas in Jess's head. Stacey's loss of her child makes Jess want to have another baby, and she and Sam do that, adding baby Kyle to their family. Stacey also suggests to Jess that she and Sam should remodel the house, which they decide to do.
In reality, Stacey has been possessed by a demon (the very same demon that Dean created in Hell, the one whose creation broke John's deal and freed him, broke the first Seal and set Lilith free). This demon has two aims; to ensure that Sam has an offspring who can act as a substitute vessel for Lucifer in Sam's place (because apparently its fate for Lucifer's true vessel to be from the Winchester-Campbell bloodline) and to ensure that the warding on the perimeter of the house is broken so that demons can enter Sam and Jess's home (Stacey has never entered their house). Through possessing Stacey, this demon accomplishes both these things; suggesting the eventual remodelling which breaks the warding, and more disturbingly, murdering Stacey's child to ensure Stacey and Jess will form a bond that will lead Jess to want another child of her own.
The break in the warding enables Lilith to contact Sam via his dreams, however the warding on Sam's ribs still causes problems for her. Sam doesn't fully recall details of the dreams he begins having, remembering only that they are unsettling dreams involving a blonde woman who isn't Jess.
Additionally, although Dean had instructed that Angels guard Sam's home, the two angels assigned are no longer at their posts. This, combined with the broken warding on the house, enables Stacey to enter the house and abduct both Jess and Kyle when Kyle is 6 months old.
Sam is alerted to the fact that Jess is missing when he receives a call that she hasn't picked up Deanna from kindergarten. When he gets home, he discovers Eric alone in the house in his crib and both Jess and Kyle missing.
Unbeknownst to anyone, Stacey has delivered Jess and Kyle to Lilith. The demon then leaves Stacey's body. Stacey is left traumatised, not having complete memory of what happened (or even that her son is dead) and is later admitted to a psychiatric hospital.
Meanwhile Sam is distraught, calling in police and others, insisting that Jess has been abducted. However, finding no evidence to support this, the authorities record it simply as a domestic dispute/missing person's case.
Sam is certain there is something unnatural about the disappearance and knows instinctively that he needs help from Dean. He doesn't suspect Stacey at all, due to her prior mental health issues, and instead focusses on tracking his brother down.
Sam manages to track Dean down, rents a family friendly vehicle and takes his remaining children (Deanna and Eric) and their family dog across country in a desperate drive to get to Dean.
Dean has just finished a case to stop one of the Seals from being broken and is holed up for the night in a motel.
This is the point at which Sam re-enters his life.
Sam tells Dean that Jess and their youngest son are missing, and that he knows there is some supernatural cause. He senses that Dean knows more than he lets on but doesn't get an opportunity to pursue it as Dean deflects his questions.
Dean agrees to help Sam locate Jess and Kyle, initially hoping that the disappearance isn't related to any of what is happening with regards to the Apocalypse. He tries to contact Cas but is unable to.
On their first meeting, Deanna and Dean instantly bond. Sam has previously shown Deanna pictures of Dean and has spoken about him, so Deanna already feels close to her uncle (Dean).
Dean takes everyone in the Impala and drives them to the Roadhouse, which he considers to be a safehouse, given he trusts the people there and that the place is heavily warded.
In the short span of time during the drive to the Roadhouse and then witnessing Dean's interactions with everyone at the Roadhouse, Sam instantly observes a change in Dean from the person he knew a few years prior. During the night he encounters Dean in the middle of a severe nightmare. This coupled with Dean's demeanour and behaviour towards others leads Sam to realise there is something seriously wrong with his brother.
Dean leaves Sam and the children at the Roadhouse and returns to Sam's house alone to investigate the disappearance. There, he is finally able to get a hold of Cas. Cas doesn't know why there are no Angels on guard at Sam's home and, more worryingly, doesn't know what has happened to Jess & Kyle.
Dean is irate & informs Cas that the only reason he was considering being Michael's vessel was because he was ensured Sam would be kept safe. He expresses his doubts and frustrations about how Heaven treats him. Cas assures him that he will go to Heaven and find out what he can and that he will help him to find Jess & Kyle. He then leaves to find answers from Heaven.
Dean's investigation alerts him to Stacey's behaviour and his instincts tell him it warrants looking into. He heads back to the Roadhouse, tasking Ash with locating Stacey.
In the meantime, back at the Roadhouse while Dean has been gone, Sam feels isolated from the others, realising that he is no longer a true hunter. He also sees a side to hunting he hadn't known existed; a well organised network, rather than the solo hunting expeditions he was more familiar with growing up. He tries to get more information about what is happening, but people don't confide in him. He finally corners Bobby, forcing him to reveal what has happened to Dean. Bobby fills him in on what he knows from the past few years, telling him that Dean went missing, no one knows where or what happened to him in that time, but that he came back changed, angry and withdrawn. He reveals that John was killed by the same demon that killed Mary (i.e. Azazel), that Dean killed Azazel, that Jake is at large, and that they (at the Roadhouse with Dean) are trying to avert the Apocalypse. He omits mentioning anything about Angels. He also confirms that something is wrong with Dean, but that Dean won't let anyone close enough to help him.
Sam is concerned that Dean won't open to him, but Bobby reassures him that if anyone can get through to Dean, it's Sam. He also reassures Sam that the two brothers have a special bond that can weather anything, and that Dean will always have a special place in his heart reserved for Sam.
When Dean returns to the Roadhouse, Ash locates Stacey at a private psychiatric hospital, and Sam and Dean head out to question her.
Meanwhile in Heaven, Cas tries to locate the two Angels (Tamiel & Turiel) who had been assigned to protect Sam. Cas has a feeling that Heaven is less pure or pristine as he remembers but brushes this disturbing thought aside. He finds Turiel banished to the outskirts of Heaven and is shocked at the fragile state of this once mighty angel. Before Cas can get any real answers from him, Uriel appears and fills him in, alleging that both Tamiel and Turiel were traitors to Heaven, that Uriel confronted them and while Tamiel was killed Turiel was captured and wishes to repent and is therefore being 'rehabilitated'.
Cas is dubious about the allegations and about the methods by which the confession was obtained. He also questions why other angels weren't posted to protect Sam & his family but Uriel brushes this aside, revealing his disdain for humans in general. He suggests that Cas's concern for humans may be a sign of his swaying loyalty and reminds him that being loyal to anyone or anything other than Heaven is blasphemous. Cas in turn reminds Uriel that being disrespectful to humans, and towards Dean in particular (who has been charged with leading Heaven's army but who Uriel considers only to be worthy as Michael's vessel) is also blasphemy.
Uriel shrugs this all aside and instead tells Cas that something or someone has altered time and it is Cas's job to question the Fates to discover what has happened and whether it has anything to do with the Apocalypse. He also suggests that Cas work harder to get Dean back on track.
Back on Earth, Sam and Dean uncover that Stacey had been possessed by demons. On the drive back they stop at a motel where Sam has a dream in which he encounters Lilith. This time he can remember the dream, in which Lilith tells him that she has Jess and Kyle, that Jess will be returned to him, but that she wants to exchange Kyle for Sam. She explains that Heaven's power may be weakening which is why she can get through to him (referring to the scrawls on his ribs not being as potent - a reference which Sam doesn't understand). She also hints at Stacey having been possessed by a demon created by Dean. She goes on to tell him that he is the one they want not Kyle, since Kyle isn't taking the blood well, and suggests that Azazel made a mistake when he didn't mark Sam. Sam doesn't understand but instantly offers himself in exchange for his son's safety. Lilith suggests that she will tell him when the exchange will take place, and in the meantime, to show him that this is real and not just a dream, she will return Jess to him.
For once Sam remembers the dream upon waking but before he can reveal any of it to Dean, he receives a call alerting him that Jess has been found and has been admitted to a hospital.
Sam and Dean race to get to Jess. She is in critical care, the doctor informs them that her injuries are extensive, that she was severely beaten, that no one saw who dropped her off, and that Kyle was not with her (and is therefore still missing). The doctor also queries Sam about the strange markings on Jess's ribs which Sam obviously knows nothing about, but which Sam realises from his brother's reaction, that Dean seems to be aware of.
While Sam is in the room with Jess, Dean calls for Cas who this time instantly appears. Cas doesn't reveal anything about the conversation in Heaven at this point.
When Sam emerges from Jess's room, Dean suggests that Cas can help heal Jess. Sam is distrustful of this stranger and angry that Dean seems to have been keeping secrets, confronting him about the markings on Jess's ribs accusing Dean of knowing more than he is letting on.
Before Dean can deny anything, Cas explains that the markings are wardings and that he placed them on all of their ribs at Dean's request.
Sam is furious at Dean for going behind his back and interfering with his family and punches Dean, suggesting that what has happened to Jess and Kyle is because of something Dean is mixed up in. He refuses any further help from Cas or anyone else that Dean knows.
In order to end this argument and move things along, Cas reveals himself as an Angel of the Lord.
Sam is initially shocked but recovers quickly and allows Cas to heal Jess.
Cas then transports Jess back to the Roadhouse while the brothers return in the Impala.
During the return journey, the brother's stop and argue since Sam is still furious about all the secrets Dean has kept and is continuing to keep, and about the fact that John may be burning in Hell (Sam still suspects he is somehow the cause of John's death).
In the argument Sam reveals that he was dying of cancer, a revelation which shocks Dean. Dean admits that John was in Hell but insists that he no longer is. Sam manages to join the dots and realises that Dean went through the Gate and entered Hell in order to save their father.
Dean doesn't deny this but insists that he is coping with having been in Hell, and that Cas pulled him and John is also out so there is nothing for Sam to worry about. He also tells him that no one else knows all this and that Sam should keep it to himself.
While Sam acknowledges some aspects of this, he refuses to accept that Dean is doing fine, insisting instead that Dean will eventually have to confide in him because Sam won't give up on him. They continue their drive back to the Roadhouse.
At the Roadhouse, Sam questions Cas and discovers that while John is no longer in Hell, Cas was not the one who rescued him. He gives no further indication as to what the cause of John's reprieve from Hell might be.
Cas and Dean talk and bond as friends, during which Cas confides that time has been altered and that he will question the Fates about this. Dean vents some of his frustrations about Heaven and his feelings of being powerless to stop things from happening.
Sam calls a meeting with Cas, Dean and Bobby in which he tells them about the dream. While initially Dean is skeptical, they all believe Sam when he mentions Lilith by name.
They fill Sam in on some of the details, telling him that Lilith was the first demon created by Lucifer, and that Azazel had been feeding children his blood, which is presumably what Lilith is now doing to Kyle with her own blood.
Sam is shocked and disgusted to learn that not only might Lilith be feeding Kyle her blood, but that Sam himself may have been fed Azazel's blood and therefore have infected his own children by passing his blood onto them.
Dean argues that Sam was never infected with Azazel's blood since he didn't develop any special powers like the other special children. Sam confirms this, telling them Lilith suggested Azazel had made a mistake with him. This still leaves the mystery of why Mary was murdered by Azazel and why Lilith wants Kyle.
Cas informs everyone that Lilith will probably want Kyle to be Lucifers vessel. During the ensuing argument/discussion Bobby accuses Dean of having agreed to being Michael's vessel, an accusation which Dean doesn't deny. At the end of the discussion, they still have no answers.
Dean decides to contact Crowley since Crowley might know what Lilith is up to. Dean and Crowley have an uneasy alliance since neither want the Apocalypse to begin, however Cas makes it clear that Heaven doesn't approve of Dean working with a demon.
Sam & Dean meet Crowley, who gives them details of John's deal. Sam realises the deal has been broken and both he and Dean realise it was broken because Dean got John out from Hell.
Crowley tells them that it is fate for them to be possessed by the Angels, Sam by Lucifer and Dean by Michael. Sam realises that Crowley and Dean are working in alliance to stop Lilith, and to Sam's horror, Dean allows Crowley to leave unharmed.
Sam is appalled that Dean is working with a demon. He blackmails Dean (by threatening him with a truth-serum style spell) into telling him what happened to him in Hell.
Dean finally relents & tells Sam what happened in Hell, and that he tortured souls in order to secure John's release. He also reveals his feelings of worthlessness and shame etc. Sam tries to convince Dean that he is a good person, with Dean's revelations only making Sam more determined to help his brother to heal. It also solidifies Sam's belief that Dean needs help and that saying yes to Michael is a suicide mission/way out for Dean.
Meanwhile, Cas meets with the Fates who confirm that something in the timeline has been changed, however they refuse to elaborate or to fix/undo it, suggesting instead that not only has time be altered multiple times, but that it is natural for whatever or whoever is doing it to change events in time. They also suggest that time/events will be changed and redone once more. They refuse to give Cas any details of what has been altered, however one of the fates seems to give Cas additional information – suggesting that it may or may not have something to do with Mary and John, and that the only one who would know what happened the night Mary died (or what John was doing that night) would be those who were there. She also suggests that Cas can get those answers if he pursues it but that it will make no difference as things will be ending soon regardless.
Back at The Roadhouse, Dean is even more distant from Sam and the others, actively trying to avoid people. Sam realises he needs to get back into hunting if he hopes to be able to protect his family and if he hopes to heal the rift with Dean/get Dean to trust him again.
Although frustrated by the Fates, Cas returns to the Roadhouse and tells Sam and Dean what he has learnt, leaving shortly afterwards to report his finding to Heaven.
Dean decides to go on a hunting spree to alleviate some of his anxiety – Sam accompanies him, much to Dean's annoyance. The hunts go successfully, feeling to Dean like old times, and the brothers finally bond (Sam saves Dean on one of the hunts - proving both to himself and to Dean that he is still capable of having Dean's back). Sam finally manages to convince Dean to postpone saying yet to Michael and allow him time to find an alternative way to kill Lilith and avert the Apocalypse. Although Dean agrees, he makes it clear that the reality is there may be no other choice.
In Heaven, Cas reports his findings to Uriel, however during the discussion, Uriel lets slip details about the night Mary died (alluding to the fact that John was asleep in front of the TV); this alerts Cas to the fact that Uriel may be untrustworthy – the Fates implied that only someone who was present the night Mary died would have details of it. Cas then decides to question Turiel since he no longer trusts what Uriel has been telling him. Cas 'mind-melds' with Turiel, discovering that Turiel and Tamiel were not traitors and that in fact Uriel is the one who has been lying and betraying Heaven.
Back on Earth, Sam has another dream in which Lilith suggests that if Sam or Dean kill Jake, Lilith will return Kyle. Though Sam doesn't believe her, it makes him realise that she thinks of Jake as a threat and that perhaps they can join forces with Jake to defeat Lilith.
Sam and Dean arrange to meet Jake in the hopes of forming an alliance or at least, finding out more about why Lilith wants Jake dead. The meeting does not go as planned, Jake seems deranged and is determined to kill Sam, believing that Sam is trying to take over from him (Jake wants to be Lucifer's vessel since he had been promised power etc. by Azazel, but now realises that Sam might take that from him). He also possesses psychic abilities derived from drinking demon blood (supplied by Ruby, who is also present). Dean shoots Jake with the Colt but Jake is merely injured; since he is not a true demon, he is not killed by the bullet, however since he is empowered by imbibing demon blood, he is no longer entirely human either and therefore manages to recover quickly.
While Jake is incapacitated, Ruby attempts to pick up where he left off in killing Sam. Dean manages to start an exorcism and call out for Cas. Cas arrives and is able to fend off Jake but not kill him since Cas is weakened from what he has been doing in heaven and Jake is too powerful. He, Sam and Dean manage to escape and return to the Roadhouse.
Michael visits Dean during a dream and, having become tired of waiting for Dean to say yes, begins to torture him. Sam and Cas manage to wake him before the torture can continue further, and Cas wards all their ribs preventing any angels (including himself) from tracking or contacting them.
Since returning to the Roadhouse, Sam has been plunging into research to find something that will help them – he uncovers details of a book of ancient spells allegedly revealed by an angel (the Book of Soyga). Cas retrieves the book, and it transpires that no one other than Dean can read it, but even then, the text is only visible to Dean when Dean's blood is spilled on the pages. They begin the process of decoding the book.
Cas also questions Dean about the night Mary died, wanting to confirm what Dean knows about John's whereabouts. Dean confirms that while he doesn't know exactly where John was, he assumes John was asleep in bed. For Cas, this information confirms Uriel's involvement in Mary's death (since Uriel said John was asleep in front of the TV, a detail only someone who was there that night could have known).
From decrypting the book, they uncover a spell which will give Dean the power of Michael without having to say yes to Michael (i.e. without having to be Michael's vessel). The spell requires Dean to drink Angel blood (as opposed to Demon blood, which was what Sam needed in canon). The amount of blood needed will inevitably kill the angel whose blood is used.
Cas says he can help. Dean initially assumes that Cas is volunteering to sacrifice himself, but Cas reveals there is a traitor in Heaven. He believes they can trick this traitor into coming to Earth, where they will trap him. Initially it seems that Cas was talking about Turiel, since when they set the trap, it is Turiel who appears. But it turns out that both Cas and Turiel have been working together to bring down Uriel.
When Uriel is trapped, he confesses that he killed Mary and took on the appearance of yellow eyes/Azazel in order to ensure that John would become a hunter and therefore raise Dean to be a hunter. He wanted Dean to be raised as a hunter since Dean was going to be Michael's vessel and lead Heaven's armies and therefore needed to be trained as a warrior. He also reveals that he has since changed his allegiance from Michael to Lucifer, since he believes Lucifer is the only one who truly loves Heaven, and also because Uriel loathes humans and believes, as Lucifer does, that Angels are superior and Heaven belongs to them, not humans.
Turiel and Cas continue their interrogation of Uriel, but some of Uriel's supporters arrive to free him. In the skirmish that follows, Dean, Sam, Turiel and Cas manage to survive, with Uriel and the other angels who came to help him being killed.
With Uriel dead, Sam and Dean are back to having no angel whose blood they can drain, and Cas offers to sacrifice himself once again to allow the spell to be completed.
And that's the road so far...
AN: While I do have reasons as to why there has been a long gap, I won't make excuses, I just want to apologise. I WILL finish, the end was always written, it's just the few chapters before then that I haven't got down.