The Bamboo Rats

The Great Bloom
The tiny land of Ghanzu lies in the northern portion of Bhaikkir, in the eaves of the Lizuyung Mountains. Ghanzu is home to the peaceful rice-growing folk known as Shingluhng. The Shingluhng live quietly for the most part; they have nothing of desire for the savage raiding peoples who war in the areas around them, and the traders from the Cities need not come there because there is plenty of rice in the Cities already. But every 45 years, from the earliest memory of the oldest Shingluhng, there occurs a time of great suffering known as the Great Bloom.
Ghanzu is covered (except for the fertile villages and rice-fields of the Shingluhng) in wild bamboo forest; it is quite beautiful and strange, the quiet and odd stillness of the bamboo aisles. But every 45 years, the forests of bamboo throw out blossoms, and these blossoms bloom.
The blooming of the bamboo forests is quite beautiful, but the Shingluhng regard it with fear- the blooming of the bamboo forests means one thing to them- famine, and terrible hardship. For when the bamboo blooms, the rats come.

The Rats of the Forest
The rats of the Ghanzu forests are huge, the size of a dog, and voracious. At any time in the Ghanzu one may come upon these bamboo rats, who trundle the wood in their particular way. But during the Great Bloom, the rats multiply, tenfold, twentyfold, thirtyfold, one-hundred-fold, and in great hordes they sweep through the bamboo like a forest fire, devouring all in their path, wild with hunger and frenzied savagery.
These rats storm from the forests, and the Shingluhng can only watch as these hairy beasts destroy their rice-fields, devouring every scrap of rice and smashing open their storehouses. The rats are unstoppable; the Shingluhng have tried, in the past, all manner of schemes to protect their precious crops.
But while the forests bloom, there are months of hideous famine and hardship; few of the Shingluhng survive the Great Bloom (which in large part explains why they are not a populous folk).

The Plan of Shormtungah
Shormtungah, the chieftan of the tribes of the Shingluhng, was born during one of the Great Blooms, but was delivered from the starving body of his mother. He remembers the dark times of the Great Bloom, but only vaguely. And Shormtungah has the great audacity to suggest something amazing- that the Shingluhng can be rid of the bamboo rats forever. The elders of the Shingluhng scoff at this; to them, this is like suggesting banning evil, or outlawing the thunderstorm- the gods ordain the Great Bloom, so it must occur, regardless of the desires of man.
But secretly, Shormtungah traveled beyond the land of Ghanzu, and went as far as the Cities, and in his time he returned with an ancient scroll which revealed to him something sinister about the Great Bloom, a secret hidden from his people that he believes is the cause of the Bloom...

The Tomb of Hueh-Ruhh
The scroll which Shormtungah has read spoke of the ancient being known as Hueh-Ruhh, a name given to it which means 'That Which Devours Whole'. Hueh-Ruhh was a dark being which dwelt in the west, in the wilds beyond the Ssivair Cliffs. It lived in a deep, foul cavern and demanded of the folk who dwelt in those lands a sacrafice, every 45 years. And if the sacrafice was not to Hueh-Ruhh's liking, it sent forth upon these folk a plague to bring them horror and famine- a plague of rats.
Eventually, the people could stand it no longer. They gathered together their wealth, and purchased the aid of Taunggyi, the Sorceror of Pirhang.
Taunggyi, with funereal ritual, stood before the cave of Hueh-Ruhh for ninety days. On each day he was assaulted by a horde of rats. On each day he fought back the rats with his magic, and performed an ancient ritual which drives forth evil spirits. Finally, on the ninetieth day, forth from the came came a hideous bellowing, and from the cave emerged Hueh-Ruhh himself, a hideous and terrible Nonman, a foul, hairy being which ruled in the antedeluvian days when men were as apes.
Taunggyi the Sorceror held back the horrible ancient monster, and fought it's dark magics with his hoary knowledge. And then, when the monster's guard was down, Taunggyi struck it with a dangerous paradox, and Hueh-Ruhh was slain.
But there was a problem- Hueh-Ruhh's body continued to release great quantities of blood, and from this blood was born great evil rats, hideous things that were ravenous and devouring.
Taunggyi announced to the people that he knew the solution; he took the body and had fashioned a sealed iron cart, and put the body within. This cart he harnessed to supernatural horses, and he took this cart far away, far away indeed, across the badlands (where in some distant age the Cities would be) to a small, forested valley in the eaves of the Lizuyung Mountains...

Where Do We Come In?
The last two groups of warriors who Shormtungah have sent into the wood have not returned. The mercenary witch-hunter who Shormtungah hired also did not return. One of the wise elders attempted to exorcise the forest of the evil and found his house full of bamboo rats for his trouble.
Shormtungah has decided that he needs seasoned fighters, and would rather spend the money than let the evil lie. He believes that adventurers are his greatest hope (having met many adventurers during his time beyond the Ghanzu).
His offer is small- what little gold he and the Shingluhng elders possess, a tiny sum, and a vast quantity of rice.
Should the heroes accept this mission, he thanks them obsequiously, and the Shingluhng regard them as both insane foreignerse and as possible heroic saviors.

The Forest of Darkness
The heroes are dispatched into the deep bamboo forests of the Ghanzu. As they march toward the mountains, they encounter bamboo rats, who are dog-sized and vicious (though rarely at all a match for a seasoned fighter).
As they go deeper into the woods, however, they begin to see other things- shadowy humanoids lurking behind stands of bamboo, enormous masses of darkness lurking in the distance, phantom noises.
The atmosphere becomes oppressive and humid, the sky constantly overcast. The mountains become blanketed in an ominous fog. Pools of cloudy, stagnant water are found frequently, and rats are seen traveling in huge masses through the trees.
Encounters within the Forest of Darkness:
-The heroes see strange humanoid shadows watching from a distance from behind stands of bamboo. They vanish as they are approached.
-A pack of rats feast on the corpse of Shingluhng warrior. His face is frozen in a rictus of fear.
-The witch-hunter's kit is found torn open in a clearing, with each tool carefully (almost ritualistically) disassembled in an organized manner.
-An enormous looming shadow is seen smashing through the distant forest. As they approach where it was, they see that it has left a huge swath of smashed vegetation.

The Foothills
The heroes began to enter the forested foothills of the mountains. The terrain becomes rockier, and filled with ravines. Shadows seem to cling to the ground; all darkness seems darker, lights are faint and seem dull, even campfires.
During this time, the heroes begin to encounter more dire creatures- the sinister power of the evil is revealed.
Encounters in the foothills:
-Twisted, wretched beings, a mixture of rat and man, attack the heroes with loud screeches, sobbing and snarling to be killed
-Shadowy figures approach in the mist and then disappear; heroes get the feeling that someone is watching just beyond the light of their campfire
-In a copse in the forest, the players discover a huge and hairy beast, a misshapen leftover from a primordial ice age. It becomes enraged and attacks them with tusks and blunt teeth, and can only be subdued by death.
-One of the heroes drinks from his/her canteen, only to find the water tastes bitter and metallic- the heroes then discover that in the night, their water has transformed to sludgy poison, and their food to thick rotting matter.

The Tomb of Fear
The heroes brave the foothills and reach a dark defile in the side of a cliff, a craggy wound in the rocks hidden by bamboo trees.
The ravine's walls are carved deeply with ancient heiroglyphics whose meaning is obscure. The overhanging walls make the place nearly as dark as night- if it is night-time, the darkness is impenetrable and cannot be braved.
At the end of this ravine, there is a stone stairway, upward to a stone door in the cliff. It appears that the heavy slate doors were once barred with a slat of iron, but it lies twisted on the stairs, and the doors are flung open.
Rats issue forth from the dark cavern in small packs, exiting the canyon into the forest. At some point, a hideous gibbering issues forth from the doors. A sorrowful screech marks the exit of a hideous half-rat being, which appears to be flung forth sobbing upon the steps to crawl away.
The heroes creep into the tomb. Strangely, the rats who exit the place seem oblivious to their presence, even if attacked.
The tomb is a rough-hewn passage which winds deep into the cliffside. It gradually joins a natural cavern which is full of deep pits surrounding lightless natural lakes. Around these lakes, dead things lie in heaps, bones as well as rotting remains and grey heaps of decomposed substance. Many of the corpses are rats; rats swarm the passageways and ledges of the cave, as if desperate to escape the confines of the place.
At the end of the cavern, the heroes come to the deepest pit of all. Mounds of dead things lie on the shores of the lake in this pit, and water is grey with the filth of decaying matter. A veritable mat of rat corpses floats atop this lake like pond scum, their bodies rotted together into a loathsome and disgusting mass of hair and fleshy slime.
And yet, it seems that this place of death is also the genesis of the bamboo rats, and the hideous rat-like things which infest the forest- on the other side of the lake, there is a crumbled tunnel in the wall of the cavern, from which the rats pour like a stream, and from which, once, a loathsomely man-like rat screams as it collapses into the water, thrashes helplessly, and drowns.

Hueh-Ruhh
The heroes bungle their way into this tunnel. The way is lightless; the seething horde of rats pushes back against their advance, even though they cleave their way forward with weapons. The stench of the place is abominable, impossible, and the air is hideously wet and sweltering.
The tunnel winds upward and then into a small chamber, deep beneath the mountains.
Here, the heroes witness the true evil of the bamboo forest.
Atop a natural dais in the center of the cave, there is a leaning thing. If it stood, it would be probably 8 or 9 feet tall; it's arms are limp against the stone floor, it's legs are crossed beneath it. Most of what can be seen is made up of hair long, filthy, grey and black hair, so long that it sweeps the ground. The thing's face, chest, and belly have collapsed into the body in a hellish mass of putrescence. Tangled in this mass of hair and rotting flesh are the rotting bodies of rats and human beings and man-like things; on the whole, it resembles the semi-mummified, rotting, waterlogged corpse of a gigantic ape which has become the grave of a thousand rotting dead things, and forth from the cavern of it's belly issues the endless stream of rats and rat-things, most of which snarl and scream in fear as they fight each other to be free and become tangled in the mass of the thing, dying a horrible death. Those that escape make up the tide of rats which flee the cavern.
This thing, then, must be Hueh-Ruhh. And as the heroes watch, this being comes alive.
Unimaginably horrible, this being staggers to it's feet, a gigantic swaying mass of bloated rotting flesh and hair, spewing rats from it's distended belly, and dripping streams of filthy grey water. As it smashes toward the heroes, they realize that only by destroying this thing, Hueh-Ruhh, can they put a stop to the devastation of the bamboo rats.

The End of the Rats
The battle is terrible; the creature seems impossible to harm, even with fire, and is disgustingly strong. But blow after killing blow finally fell the undead abomination, which falls to the floor in a heap of rot and immediately boils up a great cloud of putrescence. The tide of rats ceases forthwith, and before the heroes' eyes, the body of Hueh-Ruhh decays into sifting dust with astonishing rapidity. The wind of decay which rises from it's body, sweeps forth from the chamber and through the entire tomb, and out into the forest.
As the heroes exit into the bamboo wood, they see that the darkness has been banished, and the rats are gone.

Notes
Based on the strange phenomenon of Mautam, which actually does occur in northern India- http://en.wikipedia.org/wiki/Mautam