Although he appears only in shadowed silhouette and is never identified by name, Jorah the Explorer made a brief but memorable appearance on the Season 7 premiere, "Dragonstone." But why is Jorah at the Citadel on Game Of Thrones? He seems to have been locked up, and the status of his fatal case of greyscale isn't looking good.
The presence of Dany's former adviser on the far side of Westeros came as something of a surprise to viewers, considering that the last time fans saw him, he was parting ways with his queen somewhere in the vast stretches of the Dothraki Sea in mid-Essos. Daenerys ordered Jorah to find a cure for his disease and then return to her side — and while some fans theorized that Jorah's quest would take him back to Quaithe (the mysterious masked woman he encountered in Qarth), it appears that it has ultimately taken him in the exact opposite direction: the Oldtown, and the stronghold of the maesters.
All in all, this shouldn't come as too much of a surprise; after all, the only other character on the show known to have survived greyscale was little Shireen Baratheon. In Season 5, her father Stannis recounted the story of her childhood illness, in which he tells her that he called upon every maester in the land to help save her life. And if the maesters could miraculously cure greyscale once, it makes sense that Jorah would seek them out to do it again.
In that regard, his incarcerated state is probably less ominous than how it's played during the premiere. It's unlikely that Jorah has been captured and locked up by the maesters, and more probable that he was quarantined of his own free will, out of fear of infecting the rest of Westeros with an incurable disease. (Readers have been theorizing for years that an outbreak of a greyscale epidemic in Westeros is inevitable thanks to the infection of Targaryen loyalist Jon Connington. Although that character didn't make the leap from page to screen, could Jorah ultimately fulfill the same tragic purpose?)
But there are a couple of fan theories floating around that Jorah's storyline won't be as simple as "cured by maesters, returns to Daenerys." He might have to seek more extreme remedies before he can reclaim his place at Dany's side if the maesters aren't capable of replicating their success with Shireen. One possibility is that Jorah will be adopting a mysterious plot point from a book character who's not on the show: Victarion Greyjoy, another uncle of Theon and Yara who, after his hand is wounded and infected in battle, has the appendage magically healed by a Red Priest. Although it saves his life, the priest's magic also leaves his armed looking cracked, charred and blackened — and, weirdly, makes it stronger than it was before.
Although it's difficult to tell in the one brief, poorly lit glimpse we get at Jorah's arm, is that just the skin of a man with advanced greyscale? Or does that arm perhaps look more charred and blackened than the scaly grey Stone Men that Jorah and Tyrion encountered in the ruins of Old Valyria? Has Jorah already been cured of his greyscale by magic? If so, that might explain why the magic-averse maesters locked him up. And given that Jorah has already taken on aspects of excised book character Jon Connington, it's entirely possible that he's also taking on aspects of another book character who didn't make the cut.
Another theory pertains to the book Sam is seen reading in the Season 7 premiere. Although the focus of the scene is on Sam's discovery that Dragonstone is home to a vast wealth of dragonglass — which will come in handy for his buddy Jon's brewing war against the White Walkers — a close look at the page he's reading reveals a fragment of a sentence: "administered dragonglass as a cure for…" Could dragonglass somehow cure greyscale? Perhaps cutting off the infected portion of the body with an obsidian blade somehow halts the progress of the disease?
If so, this development makes a certain amount of narrative sense. Season 7 seems to be building towards a convergence around Dragonstone (making the title of the premiere very appropriate): Daenerys and her troops are already there, Euron is potentially headed to the island to procure his "gift" for Cersei, Melisandre is heading south and may find herself drawn to the Dragon Queen, Cersei will probably assault Dany's forces there, Jon will have to head there to gather weapons to use against the White Walkers… and now Jorah could be setting his sights on Dragonstone as well, in attempt to cure his greyscale with dragonglass.
Of course, Jorah will do absolutely whatever it takes to find his way back to Daenerys. Whether it involves blood magic or severing his own limb, he won't hesitate if it means seeing his beloved khaleesi again.