I echo most of what has already been said. This is a round and round good throw in plot for any scenario. It can even work in a sci-fi setting like Firefly, Fading Suns, Babylon 5, etc with minor modifications. Such is the role of a good sub and plot. (just for thinking that I threw in another .5 for its functionability)
To me what makes this such a good plot is not that it is a basic, enter bad guys, thwart bad guys, find out good guys could be actidental bad guys due to motives but that it could be a one or two shot side plot thrown into a much larger game or it could turn into a grand scenario when the players only intended to stay for a few days in this waylaid town. Kudos.