Dark Clouds Gather is an AD&D adventure for levels 7-9, produced by TSR UK. There is a lot going on here, and there are cloud giants in it, so that's my excuse to read through it thoroughly now. Plenty of people suggest the TSR UK stuff is better than many of the US-produced modules of the time - let's see.
|Flying scimitar-baboon wants you dead.
The ancient backstory here involves an archmage (Devral) teaming up with aaracokraa and good cloud giants to deal with the evil mind-witch Yesorkh and her winged baboon henchmen. Yesorkh was defeated and trapped in a gem, but now has been freed by an irresponsible cloud giant. Obviously her plans for world domination pick up where they left off, and we have our adventure.
The hook as presented involves the PCs coming upon some townsfolk trying to kill an aaracokra that they presume is a demon. Already converting this adventure to 5e assumptions is out the window, isn't it. The heroes witness a mockery of a trial for the feathered devil; if they intervene, they too are accused of being in league with dark forces, and we end up with a trial by combat. Obviously the PCs will win this one against the burliest villager, so now they have the aaracokra Tcho'eh as a pal, and can hear his tale.
|A memorable ascent to the birdfolk aerie.
Tcho'eh wants the PCs to come with him to Tikki-ti-jarra, home of the aaracokra, to assist with the raids on their nests. Apparently the bird-shaman saw the PCs in a vision and sent Tcho-'eh out into the world of man to find them. Help me, Obi-Wan! There's an overland trek through a mountain pass.
In the next section, the heroes visit Tikki-ti-jarra, demesne of the aaracokra where, after a misunderstanding, Tcho'eh takes the PCs before the shaman. The shaman tells the PCs how a cloud giant and his army of winged baboons ("snow demons") are wiping out the bird-folk; and that said giant operates out of a cloud castle. CLOUD CASTLE ALERT now you have my attention even more. Unfortunately, the shaman's exposition triggers the cloud castle showing up and attacking. How dreadfully inconvenient.
Several waves of ba'atun (baboon dudes) wreak havoc on Tikki-ti-jarra; the module gives details on the units within the swarm and when they should arrive, round by round. PCs can help fight them off, but the numbers are too great, and by the time the ba'atun return to the cloud castle, Tikki-ti-jarra is in ruins, with most of the aarakocra slain.
The shaman tells of a vision he's had of a flying craft shaped like a fish, which is somehow key in overthrowing the cloud giant. The PCs, able to recognize a chapter transition, agree to seek out this skyfish in hopes of using it against the ba'atun. Following the shaman's vision, off we go to see the wisdom of the giant eagles. Meanwhile, the remaining aarakocra will bury the dead and then head to the last birdfolk refuge.
|Hey look, giants!
The giant eagles understand some of the imagery in the shaman's vision, and give directions to the tower of ice that appeared in the dream. PCs head toward Mount Ederglow, help out some dwarves against frost giants (yay GIANTS), and the dwarves show the way. Lots of trudging through snowy mountain passes - you could add quite a few encounters here if you needed to, although maybe the mutant flying polar owlbears are sufficient. Since there are frost giants around and we're in the icy mountains, of course there are remorhaz. It's some kind of rule.
On the way to the skyfish and Devral's crystalline citadel, there's a nice encounter with spriggans. Gotta love the spriggans, and in this case it's combat with them, then they show up later in short-folk form to try to trick the PCs. Once in the citadel, it's appropriately got some magical traps and puzzles - this ancient wizardess knew what she was doing. There's exposition to be found here about Yesorkh as well, so perhaps the PCs can start to piece together what's going on. The point here is to get powered-up here at the home of Yesorkh's ancient enemy, Devral. PCs are supposed to get control of the skyfish craft (and maybe the glass griffon that's here as well). Time to rendezvous at the birdfolk rally point and prepare to assault the cloud castle.
You could run the whole battle with minis, and the adventure suggests keeping track using hex paper and the AD&D air combat rules. Bully for you if you do it this way! There's also a simpler version where the castle and assaulters are moving directly toward one another, but either way, you're going to have to track a mess of stuff. The PCs in the skyfish are accompanied by the remaining aarakocra and the giant eagles, the air elemental the birdfolk immediately summon (remember this is AD&D, they can do that because they are not meant to be a PC race) and the baddies have a mess of ba'atun. The individual winged baboons aren't awful - although in a pack they'd be nasty - but each unit has a leader who can shoot ice bolts and webs. I don't want to be five thousand feet above ground using wings of flying and get hit by a web spell, do you? Eventually the baddies send out some manticores as well.
Those who finally assault the castle itself have more ba'atun to deal with, as well as some hill giants and ogres. The music room in the castle contains a sentient talking harp, for extra cloud giant bonus points. Pursuing big bad Yesorkh (who is possessing the body of the cloud giant, Lachlan) you'll tangle with a pair of hasted verbeeg as well. You can rescue Lachlan's children, which is a good idea. Nasty ba'atun evil priests guarantee there are some undead to mess with here as well. Like a proper BBEG, if Yesorkh can escape, she attempts it.
|Ready for a big aerial battle?
There's a good amount of treasure here, including spellbooks. You can score even more treasure if you managed to drive Yesorkh out of Lachlan without the giant being killed. I imagine if you're a party of mid-to-high level AD&D characters, having a neutral good cloud giant with a flying castle in your debt would be pretty useful. If you're playing AD&D with gold-for-xp and training rules (but I repeat myself), you'll probably be happy at the end of this saga. Except the part where the authors say you can't steal the cloud castle. /sigh
Dark Clouds Gather is pretty great. It's got a sword-and-sorcery vibe for the bad guys, the locations are sufficiently exotic, and the magic feels magical. The least-satisfying bit is the beginning with the villagers, who are generic European types - if you moved this whole thing to the faux-Himalayas you might be better off in that respect. There's a lot of content here, I wouldn't try to run a chunk of Dark Clouds Gather for a con slot or as a one-shot, even if you trimmed it hardcore you'd be missing out. Given the snowy mountain angle you could drop this just about anywhere. The ba'atun make for cool enemies throughout. The tone in Dark Clouds Gather might even lend itself to Dungeon Crawl Classics or Hyperborea.
If you're running a game that can handle birdfolk as PCs, then this is the right module to run to unlock that option - by the end of it, the aarakocra (this tribe at least) are reduced to almost nil, so you'd have a good reason to add a birdfolk to the party to quest around and look for the other lost bird tribes (or whatever).
Dark Clouds Gather is pretty linear as-written, because it follows the epic storyline. You could tie in some side-stuff to make it feel less linear, or maybe not push the PCs as hard and see what they do. Maybe they don't help the aarakocra, and the ba'atun wipe them out in your campaign; you'll still have Yesorkh flying around as something to deal with.
|Dark Clouds Gather has nice illustrations throughout, including most NPCs.