This is post 5 out of 25 in the Cygnus Series of a September of Short Adventures.
As with quite a few others, this one has just a sketchy bit of plot to allow me to present something else: a "re-skinning" of a time-worn character class. (Thus, it works best if the PCs have not yet encountered anyone of the AD&D monk class... and if they're in a generally medieval version of our own Earth...)
The PCs are walking in the town, and they bump into a grimy hobo, who begins to paw at them and mutter some unintelligible things. He calls one of the PCs the "Grand Master of Arrows," and he asks how he can avoid the "Master of Prudence." He's clearly out of his mind, but after a moment or two, he moves such that a silvery pendant becomes visible; it's around his neck on a similarly silvered chain. The one pictured here is all I could find on Google; in the game it's probably a simple image of a man shot through with arrows. Sages or other learned folks will recognize it as the symbolism of Saint Sebastian the martyr.
If the PCs choose to attempt further communication with the hobo, they find that he can say his own name (Brother Jude), but he doesn't know much else about himself or where he belongs. He's relatively young (early 30s) and wouldn't look too bad if he were cleaned up and deloused. He wears a filthy brown robe tied up with a rope belt that looks like it's been steeped in mud.
The backstory is that Brother Jude was a Monk of the Order of Saint Sebastian, a secretive group within the Church that combats the forces of heresy and diabolism as do the militant orders of Paladins, but more on the down-low... They are, for all practical purposes, exactly like 1st edition AD&D monks, but their level titles are different. They wear nondescript brown robes with rope belts dyed in various colors to denote their rank:
(Modern initiates of this much-debased Order include M. Corleone and T. Durden.)
Back to game-time: A few weeks ago, Brother Jude had completed his 9th level tasks and was readying himself for the challenges of 10th level. (If his dirty rope belt is cleaned, it is revealed to be of a shining white color, with threads of gold.) He entered into solemn combat with the existing 10th level Master of Prudence, Brother Cyrus, and then something strange happened: after maybe 30 seconds of initial feints and blows, Jude collapsed in a heap. He was unconscious for several days. Eventually, he stumbled away from the Order's infirmary when nobody was looking and has been wandering, semiconscious, for more than a week.
Unknown to anyone in the Order is the fact that Brother Cyrus was born with psionic abilities. He reached his current rank by careful and judicious use of this power in combat; too much would arise suspicion. But Brother Jude was known to be the best fighter of his generation, and he was about to reach a level where he would be taught to resist mental attacks. So Cyrus took the chance to do two things: (1) he feebleminded Jude with a standard psionic attack, and (2) he used a heretofore unknown psionic mode to induce constant pain in Jude -- specifically, he feels continual splitting headaches that even invade his sleep. A standard clerical "healing" spell may fix the feeblemindedness, but the pain seems to have no cure. Only the death of Cyrus will stop it.
Will the PCs want to infiltrate the super-secret society of the monks? Will the current Grand Master of Arrows believe anyone who accuses one of their elite brethren of such a heinous crime? DMs wishing to follow up on this scenario will want to plan out the rudimentary details of their headquarters -- which to outsiders will look just like any other monastery -- and think of a few interesting character quirks for the Grand Master.
Ah, I write all of the above, and then discover there's nothing new under the sun... See also an alternate fighting friar, a S&W cudgeling brother (with other reskinning ideas in the comments), or how about a handy handsman? Google will give you dozens more, I'm sure. :-)