Caravan and Cave

From the introduction:

For various reasons, the PC's are traveling together as part of a merchant caravan on its way to the free city Styx, originating in Socorro. Along the way, the party discovers that the merchant, the unscrupulous Tyvik Gurtson, intends to double cross all of his tag-alongs, selling them into slavery to ruthless salt miners. This fateful meeting is to take place while camped in Trader Pass, a few days out from Styx. Only together can they escape this situation, living to explore the many mysteries of the Twisted Earth...