From a forthcoming unofficial e-supplement, tentatively entitled Occultism in Theah, comes - the Abbey of Arcadia!
While at first glance, the abbey appears to be nothing more than another real-world conspiracy theory dressed up in Thean clothing, it actually contains a workable campaign seed of the "Chosen One" type.
The conventional hagiography of Santa Maria, one of the first Ten Witnesses, must go something like this:
Called from a life of sin by the First Prophet, Santa Maria found her carnal longings entirely replaced by a pure and holy love for the First Prophet and his work. She grieved greatly at his death, but honored his last command and returned to Monte Joyas to reunite with the other Witnesses a year later. They were all then filled with holy purpose, and she returned to her native lands to the west, bringing Theus's word to the Acragan peoples and inspiring them to resist their fiery Numan overlords. She was martyred at the stake after ten years of good works.
In the hills of Hainzl, in Eisen, there's a group with a slightly different take on it. The Abbey of Arcadia is built upon a gentle rise overlooking a small river; small openings at the riverbank wind back into the hill, opening into a large network of caverns and tunnels. In 1254 AV, a Benefactine monk took refuge from a storm there, and found remarkable artifacts: the miraculously preserved frame of an ancient boat, empty garments of the ancient Numan style, also in fine condition, and a book* which purported to tell of the escape of the son of Santa Maria and the First Prophet from Castille to Eisen, where his line would take up the mantle of Imperator. Amazed, the monk vowed to build an abbey on the holy site.
The relics were decried as frauds, of course, and these days one cannot find them. The abbot says, a trifle sadly, that they were handed over to the Inquisition centuries ago to be burned. The abbey, named for the (now vanished) small village in Castille from which Santa Maria is thought to have come, still holds her as their special patroness, but has pushed their heretical founding tale away as an embarrassment.
...no, of course not really.
The abbot, prior, and other officials of the abbey all believe that they are guardians of the bloodline of the First Prophet. The abbot will not select for advancement any monk who does not subscribe to these beliefs. These senior officials are rotated away to other positions in other monasteries as frequently as can be managed, expanding the eyes and ears of the Abbey. Many have served as tutors or teachers to important people in Theah and several have retired to quiet jobs managing church records in major archbishoprics and cardinalate seats. Especially church records of births, marriages, and deaths...
The "true blood" lost the Eisen throne decades or even centuries earlier. Now, with the Imperator's seat vacant, it is the perfect time to locate some of the scions of the First Prophet and test them. Surely one will prove worthy...
*Yes, a book. Not a scroll. You can make of that what you like.