This adventure uses the Basic Rules set of D&D and serves as a bridge between that set of rules and the expanded rules of the expert level.
After a well detailed background of the adventure and several tips on how to play the game using the wilderness, the characters start the adventure by being offered a job as caravan guards for a group of people selling horses.
When they arrive at the homestead of the horse merchants, they are taken right into the middle of a battle between the inhabitants of the homestead a several goblin clans. After spending a long night helping the defenders of the homestead, the characters will be asked to help recover the horses that the goblins captured during the siege. As they explore the surroundings of the homestead, the group will encounter many dangers and find clues that other homestead have been attacked by goblins. Encountering a few survivors, they learn that the guy who hired them has been captured by goblins. During their exploration, they have the chance to meet a chevall (a shapeshifting centaur) and if they help him, they can learn where the goblins are hiding and eventually, what happened to Stefan, the one who hired them.
As they rescue Stefan, the leader of the kidnappers, an agent of a secret society called the Iron Ring and mastermind behind the goblin attacks, manages to escape. As they accompany Stefan back home they learn that he was interrogated about a magical tapestry that he suspects is in his homestead. Back at the homestead, Stefan is intent on piercing the secret of the tapestry using a strange magical needle with a golden thread. The tapestry reveals the location of the Lost Valley of Hutaaka, home to a legendary people thought to no longer exist.
Stefan hires the characters to accompany him on his exploration of the valley. On the way, the group has another encounter with Golthar, the man who escaped them previously, and they have a chance to finally deal with him.
When they reach the valley, the characters realize that it is still inhabited by the Hutaakans and their former slaves, the Traldars. Both groups are at war with each other while trying to survive the horrors unleashed by their incessant wars. Tips are given to run that last part of the adventure no matter which group the characters choose to support, if they choose one. They can even play the Yojimbo game and use eahc group's hatred of the other to their advantage. Once one group becomes dominant, it will try to eliminate the characters. The adventure ends whenever the characters are forced to flee from the valley or choose to leave.
The rest of the module is dedicated to suggestions for further adventures, tips on running the adventure, a rooster of npc's and monsters as well as bestiary.
Until I read this adventure, I remembered my days of playing the game with this set of rules as my very first introduction to the game and I remembered how I instantly fell in love with it. In my memory, the rules were simple and the adventures straight to the point. I never played this adventure before and was not aware of it until I picked it up recently and started reading. Between now and then, 30 years have passed and I played several iterations of the game. Reading this I feel like the game has become quite complicated. Everything in this adventure is as good as any other, more recent adventure. You have many locales to explore, a complex plot, a villain that become a nemesis, wilderness encounters, rules on how to deal with wilderness adventuring and much more! this is a great adventure and a classic in my opinion. It uses a rich background and into details. It is impressing how many elements have been crammed into this adventure compared to more recent ones with even more pages.
With little effort, a GM can adapt this great adventure to any system using none or all of the information provided herein. If I was not already deep into an adventure path, I would definitely adapt this adventure to Pathfinder!