You start in the cave. Run in the only direction that is possible and collect Green Herb and Flash Grenade. Go further. You will be attacked be a spider-like creatures called Bui Kichwa. They are weak and extremely annoying. Get rid of them by shooting them from a regular gun.
When you run ahead, you will notice a ladder and go to the niche behind it. Destroy the vase and, on the left side, climb and get to a hidden location. Collect Topaz (Trilliant) there. Go back to the ladder (BSAA Emblem 19) and go up it.
Go over the bridge and eliminate spiders and maijins. Go to decorated door. Before you go through it, shoot the torch nearby and collect Sapphire (Pear).
Go through the door (BSAA Emblem 20) and go left. After a short conversation, go along the path till it ends. Jump down and run ahead. Destroy all objects on the left and collect items. You will reach a room with a chest with treasures inside. Open it with your partner's help.
Go left and watch a short cut-scene. When you regain the control over your character, jump down and go left. Collect items. Run left and go up to a group of enemies. Eliminate them by hiding behind the shields and watch out for the archers.
Collect Green Herb and go upstairs. Then you have to fight your way to the others. Collect all dropped items. When you reach the top of the stairs, eliminate other enemies and go right to join Sheva. You will reach another chest. Open it.
Collect Sapphire (Square) and Sapphire (Pear). Run to another location. Collect Green Herb and Ruby (Pear) situated near a skeleton. Go back and enter the corridor. You are in place where you're partner was only few moments ago. Run right and use Sheva to open the next chest. It will activate the trap. Press the proper key to avoid a hard landing.
Run down, eliminate other enemies and collect items. There is really a great number of enemies here. There are many types of enemies and they attack from all directions but if you deal with them, you will be able to collect many objects and open one of the chest situated in dead ends. Collect Ruby (Trilliant), Sapphire (Trilliant) and Emerald (Trilliant).
Take the only possible way and enter another room full of maijins. There are far away from us so you can eliminate them all without any problems by using sniper gun (BSAA Emblem 21).
After eliminating all opponents, search the location. When you reach the other side of the room, maijins will start throwing huge burning balls in your direction. You have to avoid them at all costs and use the mechanism situated in the centre of location. When you do it, you can leave the room. Door will close very fast so collect all items (if it's possible) before you open the door.
Now you can relax. Go down. Perform a simple Quick Time Event and reach the door. Open it (by pulling two chains) with your partner's help. Go downstairs and reach another location.
There are no enemies so you can search it freely. Go right. You will reach a hill on the right, jump on it. Run upstairs and collect new items. Go back, go downstairs and go left. Collect Grenade Launcher from the suit case. Run right and come up to a big statue.
Pull the chains with your partner (you have to go around the statue to do that) and unblock the further way. Go upstairs and "use" another statue ( Topaz (Square) under it).
Run over the bridge you have made. You will be attacked by few maijins. Eliminate them and run right, then left and then left again. Go downstairs and turn right. Run upstairs and pull other chains (there is Ruby (Pear) under the statue).
Run right and reach a violet statue. Your partner will wait there and you have to find another chain. It is situated on the ground floor. Go downstairs and turn left. Eliminate another group of maijins and pull the chain. There is Ruby (Oval) under the statue.
The last red statue is situated on the other side. Run onto a destroyed fragment of stairs to get there. Run up to the statue and pull the lever (there is Topaz (Square) under it).
The boss from the second chapter will appear after few moments. You have two possibilities - you can run away by running up the stairs or fight. If you decide to fight, use the same technique as before. When the boss dies, you will be able to collect Soul Gem. If you don't have enough ammunition or first aid kit, don't try to fight.