I like the premise of this adventure: heists, kidnappings, jailbreaks, burglaries and manipulating events without slaughtering everything in sight seem underrepresented in modules. The materials have been edited down to the essentials; the minimalist key for the castle where most of the key action takes place is a particularly good feature. The section on possible plans and their potential flaws is helpful. What isn't clear is how the adventure teaches the PCs the tricks of stealth, bluffing and planning etc in a gradual way. A possible solution would be a notoriety system.
A very strong prisoner rescue scenario is WGR6 City of Skulls; it makes us of a notoriety system. Bascially the PCs pick up points for who they are (e.g. elves look out of place in an evil kingdom), but more importantly, what they do (e.g. leaving witnesses, corpses lying about, broken locks). Squads of increasing power are dispatched to locate and destroy the PCs as points accumulate. This could be adapted to Kidnap the Archpriest. Asking questions without subtlety e.g. "Where are the Archpriest's rooms, and when is he least guarded?" would gain points. The leader of the squad might have a written order stating "track down the foreign traders who were in the Market Square asking questions about the Archpriest". The PCs might realise they need to be more subtle, and change disguises. Tougher squads could comprise a couple of Black Endoguards.