Return to White Plume Mountain
This was one of the greatest adventure modules out there. I played it so many times that I once used it as a Mind Palace in university, because I can remember every single room.
White Plume Mountain
The original adventure took the adventurers around a 'house of fun' style dungeon, with a ham-fisted hook, and no kind of plot. They enter a room, and beat up baddies. Sometimes those baddies have a magical weapon. One room has a big zoo of monsters in glass boxes, and the PCs must fight through them. They can't defeat the evil wizard who sits at the base, because the plot says so. The evil monsters with magical swords will fight one at a time.
The Return
Whether or not the players experienced the original crappy module, the Return obviously felt grander for having history underneath it. The area has been greatly expanded, but you can still see the outline of the old map inside the new map.
The modern map built on top of it, with the notion that many years have passed since the fun-house adventure, and the wizard Keraptis has disappeared.
Long ago, Keraptis wanted eternal life. He tried potions. He tried placing his mind in magical scrolls so that whoever read the scroll would gain all of his memories, and magical abilities. Nothing worked, and so eventually he ascended to a strange, ethereal plane, beyond life and death.
These botched Keraptis-scrolls littered his mountain-domain, and soon a little gnome picked one up and read it. Even though the memories were incomplete, he still fully believed himself to be the original Keraptis, and that he had successfully transferred his consciousness through the scroll.
An ogre read one shortly after, leading to a power struggle, then a jinn, who was once a loyal servant of Keraptis. Here the players enter a mad power struggle, with a total of four wannabe Keraptises ('Keraptes'? 'Keraptae'?), each of which have one of the magical weapons from the original game.
The Hook
Most of the Keraptis scrolls were not there to instil his full personality, but only a single spell. They were made as experiments, but since the scroll imparts no other personality, whoever reads it starts off by learning a new spell, but then slowly starts to lose the rest of their mind. They become a sort of living zombie, wandering and drooling.
If a Keraptis (or pretender) ever meets one of these walking spell-slots, he immediately gains control over them, through some metaphysical bond. Thereafter, the wizard can control the husk telepathically, and even speak through them.
All this magical metaphysics might feel like a stretch in any other system, but for D&D? Par for the course.
Once the players arrive, they will inevitably read one of these scrolls (Keraptis' gnomish followers give them out for free) and soon after find out that they have less than a month before they become a vassal for a greater mind.
The Chaos
With not much time to spare, the players must try to understand their condition, bargain with mad creatures who believe themselves to be Keraptis, and try not to piss any faction off too much. In addition to the four delusional Keraptis usurpers, a faction of those loyal to the original Keraptis occasionally interfere with the armies. If the PCs agree to embark on a mission for this group, two warriors, or even a friendly ogre may agree to join them.
All this leaves aside the rich areas around White Plume Mountain, where the group will have to hunt for a missing magical weapon - the sentient trident 'Wave'.
The Fights
Random encounters spring up now and again. Not everyone fights, so clever players might avoid combat, but whether they choose to fight or not, they will have all manner of new toys, from their new spells (from the scrolls), to the magical weapons, and potentially allies from any faction they have joined up with (or pretended to join).
Perhaps they'll take the ogre from the loyalists faction, take a boat to the delusional Keraptis-gnome, then fight against his gnoll scouts, then his ogre-guards, each of which is dressed in chain mail, and wields a bastard sword. Perhaps they'll bargain with him, and sweet-talk all sides at once, then steal the magical items they need. Or perhaps some magical tricks can sort the situation out.
Oh, and remember the menagerie of magical monsters Keraptis kept? They're all dead, but one Keraptis teleported in, and used Necromancy to raise a giant crab from the dead, then put an amulet of invisibility on him, thus making an invisible, undead, giant crab. Picture it well: one hero is lifted into the air and has the wind crushed form them by an invisible force. The others rush to help, dragging them down, or smashing the hard invisible wall in front of them. They have no idea what's happening, damage and gas-based spells won't work. Chaos and confusion reign, but the old tactics of 'hit it till it's dead' still work.
Each run-through of the adventure will go entirely differently, but the chaos will never give the DM a headache, because the possibilities really lie along a narrow track. The players must eventually engage with each of the pretenders, and gain each of the four magical items, in order to summon back the original Keraptis, which will then erase any active scrolls, and ensure they do not go mad.
Problems
Despite a very nice pace, the adventure suffers from serious issues.
Casual Racism
Every evil-gnome is black. You know they're evil, because the "racial alignment" ("RA") says "Evil". This fits entirely with the D&D pattern of skin-based morality.
- Good elves have light skin. Evil elves have black skin.
- Good dwarves have light skin. Evil dwarves have black skin.
- Good gnomes have light skin. There are also neutral gnomes (between good and evil), with 'earthy-brown' skin.
- All halflings are good, and all halflings have white skin.
The main books present these patterns, and Return to White Plume Mountain finishes it off with another piece in a puzzle that everyone's already solved by adding evil dark-skinned gnomes.
You don't have to be Dr Skinner to see where this is headed.
DM: You can see a small, dark-skinned group of gnomes in the distance.
Player 1: I shoot at the nearest one with my crossbow!
Player 2: Woah! That's super racist. Why would you do that?
Player 1: Well, I just thought they might be evil, because, um...
DM: Yes, as you know, the..."deep gnomes" are indeed an evil race.
(Side note - I once brought this up, and Reddit told me to stop being an 'SJW' and making up problems)
Despite how mental the problem seems, we can fix it by making the gnomes, just regular gnomes.
Everything's a Fight
Despite the potential for social interaction the book reminds the reader constantly that any usurper-Keraptis will not take 'no' for an answer, so very often, the players' ability to negotiate becomes stifled.
Once again, I'd encourage any DM to just ignore this, and let the PCs bargain if they can do so reasonably.
Players Must Sacrifice Allies
Many of the magical items and monsters will kill players without much thought for their hitpoints.
- The vat of life-giving ooze will animate anything it touches (making a dancing sword, or a friendly, sentient scarf), but touching it too much will kill anything.
- The complete-Keraptis scrolls will turn any player into an NPC who believes himself to be Keraptis.
- The tentacle-creatures in the lake will drag players underwater and drown them within a couple of rounds.
- If a player accepts that they must look at 'a hypnotic wall of magma', they will become a Keraptis-husk almost instantly.
- Any number of items in the magical laboratory can kill them.
- And if that lot weren't bad enough, the mountain contains the ultimate player-killer: the Deck of Many Things.
Players can only hope to avoid the random deaths by getting NPCs to 'go touch that thing'. Once they pull this trick once and see the instant death, the temptation to do so again will grow, and eventually gnomes will be able to track them by the trail of dead allies.
In this case, I can only recommend being liberal with some kind of intelligence check to figure out what an item does before using it.
End
It's pretty fun, but A,D&D isn't, so if you want to play it, you'll have to convert to some other system. No real challenge, since you can find all the NPCs and monsters in pretty much any standard fantasy book - ogres, gnomes, a sphinx, et c.
Oh, and once the players get the four items, and summon Keraptis from the strange timeless plane, they find he returns as a baby, and at that point the mountain begins to collapse.
It's a fun ending, as the night slows, everyone's safe, and the players can wind down by debating what on earth to do with a random child, and whether or not they have to worry about it becoming as evil as the original Keraptis.