I have strangely fond memories of the Dungeons & Dragons adventure module, Curse of Xanathon. I say "strangely fond," because it's not a very good module, even if one grades it on a curve, many people do. My personal fondness stems not from the adventure itself, but from the fact that it's the first D&D module a member of my extended family purchased for me.
Though my love of D&D and other RPGs was well known to my grandparents, aunts, uncles, and cousins, none of them really understand this new obsession of mine. Even my favorite aunt, who'd introduced me to Star Trek, taken me to see Star Wars, and got me Darren McGavin's autograph, took a while to fathom what roleplaying games were all about. That's why her gift of Curse of Xanathon to me on my birthday still sticks with me decades later.
Published in 1982 and written by Douglas Niles, Curse of Xanathon – or The Curse of Xanathon, since the interior text is inconsistent on this point – is the third module written for use with the D&D Expert Set. The suggested level range is 5–7, which I consider a mechanical sweet spot for D&D. The module opens with "Notes for the Dungeon Master" that are well worth examining, since they shed some light on its shortcomings:
The Curse of Xanathon is an unusual module, in that much of the players’ actions will be in the form of detective work, as they try to discover clues to the problem plaguing the town. Once they have located these clues, they will have to decide on a proper course of action. If they make wrong decisions, they could conceivably waste much time and obtain no results. You, as the DM, will need a careful touch to keep the players on the right track without making solutions and objectives too obvious.
I find it remarkable that, even as late as 1982, the conflation of "player" and "player character" is still occurring. That aside, you should already be able to see the source of the module's problems. Niles explicitly presents Curse of Xanathon as an investigative scenario, in which the characters' actions depend on the discovery of clues. Because scenarios of this sort are prone to going awry, he counsels the DM to "keep the players on the right track," even he warns against "making solutions and objectives too obvious."
Niles goes on:
Much information is included in the various scenarios, and astute players will no doubt be able to determine the proper course of action at each stage of the adventure. If a group of players is unfamiliar with this type of detective game, they may become frustrated or disinterested. The DM is encouraged to offer additional clues whenever these would seem to be necessary. This can be handled in a number of ways. For example, the High Priest of Forsetta, who moves around in a beggar’s disguise, is introduced in Scenario 1. The DM should feel free to use this character whenever necessary as a source of information and guidance to the party. He will never join in any adventuring, however!
Hard as I might wish to do so, I find this paragraph difficult to defend. While I suspect that all but the most intransigent referees have occasionally thrown a metaphorical bone in the direction of hapless players from time to time, the use of an non-player character as suggested here is a very bad practice to encourage, despite his final admonition. Curse of Xanathon isn't quite a railroad, as the term is traditionally used, but the High Priest is a railroad conductor who regularly pops up throughout the scenario to nudge the characters in the "right" direction.
The mystery the characters must investigate is the strange behavior of Duke Steven Rhoona, a previously good and just ruler, who has lately been issuing nonsensical decrees, such as that all taxes must be paid in beer rather than gold and that all horses must be ridden backwards, with the rider facing the horse's tail. His subjects fear the duke has gone mad, but the truth is he's fallen under the titular curse of the Chaotic priest, Xanathon. Xanathon is an agent of a nearby nation; he's been sent to foment rebellion in the duchy as a prelude to invasion.
As a premise, it's a perfectly fine one for an adventure focusing on investigation and intrigue and Niles does provide a number of useful tools for the referee to aid in this. For example, there are tables of rumors and tavern names, as well as an overview of the businesses and NPCs of the duchy's capital, not to mention a map. Likewise, there are five distinct sections of the adventure, each of which deals with finding or follow up on certain clues. These sections each take place in a different locale, with their own unique elements and denizens, like the Chaotic shrine and the ducal palace. The guts of Curse of Xanathon are solid, evocative of earlier location-based adventures.
However, it's clear that a sea change has overcome module design at TSR by this point. A stronger sense of "plot" has begun to creep in, along with narrative crutches like the aforementioned High Priest NPC, who pops in and out of the adventure as needed to ensure the characters keep heading toward the inevitable resolution of their tasks. This isn't full-blown Dragonlance-style "story," but it's certainly heading in that direction. At the time I was given Curse of Xanathon, none of this was at all obvious to me. Re-reading now, though, it's impossible not to see the signs of the impending Hickman Revolution and all that it would eventually entail.