The season starts off with Dean Winchester (Jensen Ackles) as a demon. Now, it should be noted that this isn't your standard Supernatural demon possession. This isn't some demon from Hell taking over Dean's body; this is Dean's soul corrupted and twisted by the Mark of Cain, something we haven't really seen before in the series. Dean currently spends his days hanging around with Crowley (Mark A. Sheppard) as the pair tear through one dive bar after another, and it seems the inhibition-free older Winchester doesn't care who or what he has to go through in order to have a good time.
Meanwhile, Sam (Jared Padalecki) spends his time trying to find his older brother. His tactics are simple, find a demon and torture information out of it until he can trace down Dean and his new buddy. The only problem is, it seems Crowley really wants to stay hidden. That is, until the King of Hell starts to realize that he doesn't have as much control over Dean as he thought he did.
The first few episodes of the season are all about not only capturing Dean, but trying to bring him back to his normal, non-demon self. Even if the Winchesters can end up back on the same side though, they can't remove the Mark of Cain from Dean's arm, and Dean finds that its murderous desires are hard to keep under control.
While this is going on, Castiel (Misha Collins) is having problems of his own. The Grace he stole in the previous season is starting to fade, and it is making him sick. When Hannah (Erica Carroll), another angel, finds him and recruits him to track down rogue angels, she starts to see just how sick he has become. Castiel knows his time is running short, and he feels he has another mission to take care of before he is done. He tracks down his host's daughter, Claire Novak (Kathryn Newton of Paranormal Activity 4 and Gary Unmarried note), only to find her in child services since Claire's mother disappeared months ago looking for her missing husband. Claire actually makes several appearances throughout the season as Castiel works hard to resolve these loose ends before what he feels is his approaching end.
Once the focus of the season shifts from saving Dean to removing the Mark, several characters return, and a few new ones make their debut. In one episode, Charlie (Felicia Day) returns from The Land of Oz. The only problem is, she isn't completely herself - she has been split in two in order to have a more ruthless Charlie to help win the war that was going on in the other world.
Bobby Singer (Jim Beaver) also returns in an episode when the Winchesters are hoping to gain some unauthorized access in Heaven. Not only does this episode give us a chance to see such a great character again, but it also gives us a bit of insight into the inner workings of the show's version of Heaven.
In one of the season's pivotal episodes, Cain (Timothy Omundson) returns because Dean hopes that by defeating the father of murder, he can remove the mark, or at least find out if Dean has any hopes of gaining control over the impulses it is pushing on him.
As for new characters, an early episode introduces Cole Trenton (Travis Aaron Wade). Apparently some years back, Dean killed Cole's father while on a hunt. While Dean doesn't remember the incident, he is confident that Cole's father was some kind of monster. Ever since that day, Cole has been training himself to find and track down his father's killer. From the moment Cole first attacks Dean, he starts to see the supernatural underworld that is all around him, but he finds it hard to accept. By the end of his four appearances this season, he will have a much better appreciation for what the Winchesters face every day.
We also get to meet an ancient witch named Rowena (Ruth Connell). She has left Europe and come to America, not only to seek power, but to also recover old spells and lore that have been confiscated by the Men of Letters, a society that Sam and Dean found themselves belonging to last season. As Rowena's role grows bigger in the season, we learn of her connections to other main characters, and it seems that she might be the key to actually removing the Mark from Dean's arm. She just needs a particularly powerful spell book that the Men of Letters stole many years ago.
Unfortunately for Sam and Dean, it's the hunt for this spell book that puts them in the sites of yet another enemy force. The Styne family claims to be large, widespread and apparently responsible for many of the atrocities to befall mankind over the centuries, and it appears that a major reason for that ability is the very book that Rowena wants to possess.
Of course, Supernatural isn't all doom and gloom, and Season 10 is no different. In one episode, a Sheriff's convention puts to recurring characters in the same room, and of course, when craziness happens, the Winchesters make an appearance. In this episode, Sheriff Jody Mills (Kim Rhodes) calls the brothers in because of what appears to be a vampire attack, but the presence of Sheriff Donna Hanscum (Briana Buckmaster) means they have to take up some old FBI identities.
In the series' 200th episode, "Fan Fiction," the brothers find themselves having to work alongside a high school theater group that is doing a musical interpretation of Chuck Shurley's books inspired (literally) by Sam and Dean's adventures. While it takes a bit of work to figure out what monster is attacking the show's cast and crew, they do get a bit of insight into their own lives, and even a few arguments over the young director's "interpretation" of how events played out after Chuck's final book.
Along with the 200th episode, the Blu-ray release of Supernatural: The Complete Tenth Season comes with a making of that focuses on the semi-musical episode. It also comes with the 2014 Comic-Con panel, deleted scenes, a gag reel and commentaries for "The Hunter Games," "There's No Place Like Home." and "The Executioner's Song." There are also two more featurettes about this show, one that talks about everything that lead up to the start of Season Ten, and one about the mythology around the Mark of Cain and related elements that are central to the season.
While all of these are interesting, there is also one more featurette that might even have the full status of "documentary." This hour-long special feature is all about the fans of the series and while it covers a lot of ground, it focuses on three specific cases. In one, a young fan of the show spends untold hours building a set of angel wings to complete her Castiel costume. Another segment apparently reaches back to the show's early years when a fan built a wooden chess set whose figures were derived from the show's main characters. It talks about this fan's artwork and what she went through to not only create it, but even present it to Padalecki at an early convention. According to the documentary, this chess set sits on a table in the studio where everyone can see it. The final story is about the acquisition, restoration and modification of a '67 Chevy Impala that was so good that it ended up being used to film an episode in Season Nine when the official version of Baby couldn't make it to the set.
Supernatural: The Complete Tenth Season is not only a pivotal season because of the resolution to the Mark of Cain problem, but also because it contains the prestigious 200th episode that is as much a love letter to the show's fans as the documentary simply called Supernatural Fans. While I wouldn't recommend jumping into the show on this season, I will say that this season is a strong one and it is worth catching up on the rest of the show (if you've somehow fallen behind) in order watch this one.