Finding Milos Premule proves to be a difficult situation: As you arrive at the popular temple (closest of the suggested locations to your inn) you find it under a great deal of hustle and bustle... The commanding priests are desperately trying to divide their time between reading letters, answering questions, instructing subjugates, writing letters, scheduling meetings, rescheduling meetings, exchanging information, while the lower-ranking priests attempt to carry out new orders, answer questions, take more orders, complete previously ordered tass, giving orders to lower-ranking priests... Eventually you find out that Premule is not here, but may be at the barracks...
It takes some trouble to get there -- it lies within the town center, an acropolis of sorts, walled and elevated from the rest of the city, and not open for foreign passage. The guard at the gate informs you that this district is limited to property-holding residents of Jance, Bethel, or its satellites, which sadly you are not. However with proper escort -- one guard per two persons -- you may be allowed to pass through the center, provided you plan to exit before nightfall. There is a cost to this, although given your mission it may be lowered (Diplomacy DC 15 to reduce the number of escorts by one, reduced by one more for every 5 above that DC... The fee is 4 sp per escort. There may be modifiers to the check depending on what argument is used, so don't mark off the silver till my word on it... If anyone's confused, can re-explain.)
Likewise you are not let beyond the front gates of the barracks without escort by a Cleric of Heironeous, which on the good side is free, on the bad side is non-negotiable, and on the worse side takes forever to be found for you. Finally you get through and find much the same situation as you found at the temple popular, magnified tenfold. With some coaxing you are directed to the fortress-temple, and after more troubles there you finally gain an audience with Father Lathias -- in a busy rectory off to the side of the main worship hall -- acting coordinator of religious and military affairs in Jance, in the absence of about six other people of higher rank, including Father Premule, who is in Bethel awaiting an audience with King Cheraul. (Technically, he would be the acting coordinator even if Premule was there, as he oversees the church as a whole, operating out of Jance, whereas Lathias' authority is Jance-specific... But regardless...) He offers to take the letter for you, and to take care that it is seen by Milos' eyes only...
By this point, you'll notice, it is nearing nightfall.
(Whew! Feel free to backtrack to any conversation through any of that, with any questions you might have, and change your course if you feel you would... I just didn't want to force you to roleplay through the big run-around you were bound to receive, considering that your intentions were pretty clear.)