At the beginning, run after Ann through the tunnel. You'll approach a large space where a flying creature will be waiting - kill him with the spear or with a couple of pistol shots and go up the stairs (picture).
You'll walk up to a spot where bushes will block the way. Ann will climb the mountain wall onto the rock shelf, in order to get the fire. While she is climbing, defend her from the flying creatures (two) by shooting them.
Once you can move on, you'll reach a place where you'll have to jump into muddy water (brrrrr). Lucky for you, Ann will run around and kill any creature that will attack you. Don't worry about anything, just swim forwards. Once you'll be on the other side, she'll give you a hand and help in getting out of the water.
While walking under the rock arch, you'll reach a large area limited by clumps of weeds. Move along the only path and pick up the spears nearby. Attack and kill all the monsters (new - I think that they where suppose to look like scorpions, but do they? Everyone has to answer that question for himself, because they look like beetles to me :)).
After a short walk you'll approach a fire, light up the torch nearby and start burning the bushes. Do it fast because it's going to rain and the flames will go out. Also, defend yourself from a couple of flying creatures (I recommend throwing spears), which will start eating dead opponents.
After clearing the area, follow Ann onto an elevation.
Once you are on the move again (you won't be attacked), approach a place where - in order to complete the stage - you have to knock down a pitcher with fire, which is above an obstacle.
At the end of the road you'll reach the rest of the crew, but you still won't be able to join them (the scarp will be the obstacle). Ask the dark skinned man for the sniper rifle (once you do this, you'll be attacked from behind, turn around immediately and kill the creature).
Next, go through the bridge that will lower down and end this stage.