At its core, Supernatural is a show about two brothers. Two brothers raised in their family business: hunting things and saving people. Well, two brothers and one car. Okay, two brothers, one car and one angel. And (formerly) one Nephilim. Actually, there aren't just two brothers, either. Technically, there are three Winchester siblings, but you wouldn't know it from Sam and Dean Winchester.
Adam Milligan, the neglected third Winchester, is Supernatural's biggest loose end. And, as the series finally drives closer to the end of its 14-year long journey, the window of opportunity to close the book on the show's most tragic character is quickly closing. And a reckoning with the brothers who gave up on him years ago could be exactly what the show needs in its final season.
WHO IS ADAM MILLIGAN?
Unlike his older half-brothers, who suffered through the demonic murder of their mother and a distant father preoccupied with avenging her death, Adam grew up in a normal, comfortable home. John Winchester fathered Adam in the early '90s, years after Mary's death, with a woman named Kate Milligan, and though characteristically absent throughout most of Adam's younger years, he began to make periodic appearances in his later ones; keeping him at arm's length, both from the hunting life and his half-brothers.
John's death in Season 4 left the ticking time-bomb of a domestic mess to explode in his wake. To make things even more complicated, the Adam that reached out to a stunned Sam and Dean two years later wasn't even the real Adam. Instead, it was a ghoul wearing Adam's face, a disguise that it hoped would lure John into a deadly trap as penance for the hunter's slaying of its parent. (John and Kate's unlikely meet-cute.)
Instead, Sam and Dean were the ones caught on its hook, something the ghoul probably came to regret after the heroes took their own revenge out on the monster that devoured the brother they never knew they had. Sam suggested that they get Castiel to work his angelic revival magic over Adam but Dean decided, given the situation, that a hunter's funeral was a better idea.
Though Dean probably had Adam's best interests at heart, this could be seen as strike one against him and Sam.
WHAT HAPPENED TO HIM?
Following his death, the real Adam Milligan went to Heaven where he was blissfully unaware of the pre-Apocalyptic war that his brothers on Earth were caught in the middle of. In Season 5, he suddenly found himself drawn into the conflict at the behest of the archangel Zachariah and his followers; angels who doggedly believed that the End of Days should go ahead as scheduled.
Sam and Dean had important roles to play as the "true" vessels of Lucifer and, his would-be slayer, the archangel Michael, respectively. However, with Dean unwilling to play ball, the angels saw an opportunity to enlist their second choice, Adam, for the job, instead.
Despite their best efforts, Sam and Dean were unable to prevent a resurrected Adam from having his consent to allow Michael possession of his body tortuously dragged out of him. The season -- and the holy war -- culminated with a Michael-possessed Adam and a Lucifer-possessed Sam falling into a cage designed to keep the Devil, and anything else, trapped in Hell.
Strike two against Sam and Dean.
WHERE IS HE NOW?
While Sam made it out of Lucifer's cage not long after his imprisonment in Season 6, without the fallen archangel or a soul, Adam was left behind in Hell. This happened again when Dean made a deal with Death to recover Sam's soul and the duo made little to no effort to try another rescue attempt.
By the time Season 10's "Fan Fiction" rolled around, Sam and Dean had to be reminded who Adam was after seeing one of the players in the "Supernatural" musical dressed as him. As it currently stands, the third Winchester brother is out of sight, out of mind.
That would be strike three against the Winchesters.
WHY SHOULD ADAM COME BACK?
After God threw the gates of Hell wide open, Season 14's finale quite literally opens the floodgates to a season-long send-off packed with returning fan-favorites. Adam might not exactly fit that description, but bringing him back into the fold -- even for just one episode -- would be a great surprise for the show's loyal fandom, who, like Sam and Dean, may have also let his existence slip off of their radars. It would also serve as a nice nod to Supernatural's original intended ending, as envisioned by creator, Eric Kripke, particularly with another apocalypse looming on the horizon.
Fan service aside, Adam's potential return would present the perfect opportunity to hit Sam and Dean where it hurts the most: family. Time and time again, we've seen the close-knit brothers risk life, limb and soul to snatch the other back from whichever grave or alternate plane of existence they've been sent to. They've never really made much of an attempt, since Season 5, to extend this courtesy to Adam.
Granted, the duo didn't have a chance to build up the same co-dependent bond with John's secret son as they have with each other. But, their fixation on family, in all its forms, makes their hypocritical absent-mindedness about Adam damning in a very literal sense. For a show built around brotherhood, it's the worst sin Sam and Dean could have to atone for.
Supernatural has long depicted its central hunters as lovable but flawed heroes whose wins only just outnumber their losses. Judging by our strike count, there's more than enough ammo for a liberated Adam to throw at Sam and Dean if he chooses to go down a path of vengeance. And Hell hath no fury like a Winchester scorned.