Warning: The following contains spoilers about the most recent episode of Agents of S.H.I.E.L.D. If you haven't watched yet, you may want to bookmark this page and return once you have. Proceed with caution.
It's powerful enough to make ghost people believe they can play god. It's dangerous enough that Daisy (Chloe Bennet) and Ghost Rider (Gabriel Luna) are willing to step out of the shadows and team up with Coulson (Clark Gregg) to find it. And it's probably Agents of S.H.I.E.L.D.'s major link to the upcoming Doctor Strange movie.
Though first mentioned two episodes back by Ghost Lucy and her undead pals who we know now got the way they are by trying to generate matter out of absolutely nothing, the hunt is officially on for this book that Robbie's Uncle Eli described as having "all the knowledge anyone could ever need" and also "pure evil." So what is this thing that is sometimes also referred to as the Book of Sins?
Well, in Marvel lore, it's just the most dangerous mystical artifact in the universe. Created by a demonic entity named Chthon, it's been at the center of the darkest magic, responsible for creating both the first vampire and the first werewolf. Simply reading it opens the reader up to the Chthon's sinister and corrupting forces, putting the reader in danger of becoming either a vampire or werewolf themselves.
In short, the thing's bad news.
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And if you hadn't already guessed, Doctor Strange has come into contact with the book in his long comic book history, so it makes perfect sense that this dark bit of mysticism, one S.H.I.E.L.D. will definitely need some help wrangling, is coming into play just before Benedict Cumberbatch assumes the title role when the Doctor Strange movie hits theaters on Nov. 4.
As the Doctor Strange Prelude #1 prequel comic book revealed, the Ancient One's (played in the movie by Tilda Swinton) disciples have organized to protect the world from dark magic, operating under the title Masters of the Mystic Arts. They're the magical world's equivalent of S.H.I.E.L.D.—and they're the reason S.H.I.E.L.D. had no idea this mysticism existed. They're very good at their job.
However, as revealed in the latest Doctor Strange Prelude Infinite Comic—titled "The Zealot"—one of the Ancient One's disciples has gone dark. Kaecilius (played in the film by Mads Mikkelsen), in pursuit of the secrets of a mystic named Cagliostro, steals some of the Ancient One's most dangerous books, which include notes from Darkhold. It's a safe bet that Kaecilius is responsible for Darkhold making its way to Momentum Labs.
And with just a few weeks left before the release of Doctor Strange, it's an even safer bet that things are only going to get weirder for Coulson and the crew. We can hardly wait.
Agents of S.H.I.E.L.D. airs Tuesdays at 10 p.m. on ABC.