So, in outline format, here's what I've got.
I. Catching the sabertooths:
The game will start out on the savanas as the PCs have been hired by wealthy noble rancher, the Margrave Bernardo Baltasar i Morales. There should be an interesting combat as the PCs attempt to capture, but not kill, at least one adult sabertooth. Out of a pack of 3-5 (I'll play it by ear and see how well they do; more sneaking up through the grass can always pop up if it's going too easy on them.) Sabertooth stats are already present in Frostburn, but in a pinch, I can use lion or tiger stats if I forget to have that book handy or something.
II. Caravan massacre:
In a game where magical healing doesn't really exist, there may be a need to go back to the ranch and get patched up by a medic before moving on. I'll play the details of how they move into this stage of the game by ear. If they're ready to jump right into it, they can see smoke on the horizon and go investigate, or stumble across survivors. If they need to be patched up first, the survivors can stumble into the ranch in a day or two instead. Their tale is one of the margrave's important (and rich) guests on their way to his ranch, getting involved in a detour, or making a wrong turn, and ending up north of the ranch, dangerously close to Untash tribal lands, where raids and murders are common. Not only has their richly appointed caravan been thoroughly robbed and looted, but many of it's members killed, tortured, raped or kidnapped. Some of them, at least, are alive.
III. Finding the tribesmen
I'm presuming that that's sufficient motivation to go out there and see what happened; either to rescue the kidnapped prisoners, liberate their riches, or even if it's just to loot the looters and run off with the riches themselves. This will lead to a small travel vignette where anyone with any wilderness ability of any kind can attempt to track the raiders from the caravan ambush site. Some possible encounters can happen here, depending on what I think the game would best be served with: some more dangerous wildlife (short-faced bear, deadly snakes, pack of hyenas or dire wolves, a stampede of bison, etc.) and the group could run up against some other Untash tribesmen who--possibly after some fighting or at least a tense stand-off--let the PCs know that that tribe directly north (the Gisati) is some "bad medicine." As they get closer, they find that that is definitely true; there are weird creatures attached to the tribe. Mutated dogs or something. They have to fight running battles against some of these, apparently under the control of witch docter packmasters.
In a small, shallow stream valley, heavily forested, there are a number of standing stones where the Gisati make their sacrifices. Here the PCs will come across tribal zealots and worse; the witch doctor (illustrated) and Ilark Jaasru--a combination of a D&D soulknife and a Sith Lord. They might save the captives (or not--it would be dramatically appropriate yet terribly cliche for them to arrive right as the sacrificial knives or whatever are poised to come down). The most disturbing clue that they find, though--besides the witch doctor, Sith Lord, and the ghoul escort that the Sith Lord has with him (or her) is a small contingent of Untouchables, the ruling group of Tarush Noptii; those who cannot be fed upon by the vampires by dint of their caste. It seems that an incomplete copy of The Book of the Black Prince has made its way to the tribesmen as a "gift" of sorts from the vampires, along with a consulting team to make sure that the rites they use to call the Ancient Ones are done correctly.
If desired, I could even have a minor Ancient One servitor of some kind actually already summoned that the PCs have to deal with at this point. Undecided, but probably yes. That sounds nice.
V. To Tarush Noptii
Why are the vampires, or the Untouchables at least, getting involved with Untash tribesmen and sending them very dangerous books of forbidden lore? And what's a "Sith Lord" with ghoul servitors, clearly from Cannibal Isle, doing here too? I don't know yet. This is at least three, maybe four sessions out that I need to have answers to these questions, though--well, maybe late in the second session at worst. I've got a few weeks to think about this, see what the PCs do and uncover in the meantime, and like I said, I don't want to lock myself down to a plan until I see how the PCs do handle what I've got for them prior to this. So, I think I'll stop here, for the time being, and then revisit this plan after we play our first session and I see what needs to be modified and when I need to have it. Clearly this is meant to be a major hint that sends the PCs into Tarush Noptii, which will be the end of this "module" within the greater campaign, and therefore where we'll probably hibernate it for a while, so I'll want Tarush Noptii to be suitably climactic--it'll have to be the climax for the time being.