as I found out later, it clearly states that there is ONE bone devil, and you can fight and kill that bone devil either at the Baron's proclamation, OR in a random encounter in the street, OR at the temple with the pillar of flame. My party encountered the bone devil atop the tower (but couldn't hurt it, with the DM autofailing our SR checks and attacks, because he didn't want to start a big battle that night -- meaning that we started next session without our biggest spells, since we hadn't realized we were wasting them in a railroaded "can't win" encounter) AND in the street (twice) AND at the pillar of flame. So we met four bone devils and had to kill three of them. That's a bit deadlier than the normal module itself...