Your mission is to locate the soldier with the ID card. Clues are they he's wearing an orange jacket and that he's in an area where you can hear quezcatl's singing. If you forget what they sound like, use the radio to call Cecile and she will remind you.
The soldier (a CIA operative) will appear at random in one of the following areas: Catarata de la Muerte, Selva de la Leche: Hillside & Selva de la Leche: Jungle.
For an S rank run retrace your steps in the first map. In the second map (Top of Cliff) hug the right side. Do the same in the following map (Bottom of cliff). Just before the exit there is a soldier lying down: don't step on him!
In the next map, turn left immediately to get to Catarata de la Muerte.
As mentioned, the orange-jacketed soldier will appear at random in one of three maps. But on restarting he will appear in exactly the same place.
On the return journey, retrace your steps at the Bottom of Cliff, but at the Top of Cliff hug the right side. You will soon encounter a soldier facing you, but he's fairly blind so you can Mk-22 him. From there on if you keep right you will encounter no other enemies.
At the final map retrace your steps (keeping left) but be careful as you turn the corner to look directly toward the exit. The two soldiers here may be looking in your direction and will see you. Peek first.
From there on it's plain sailing if you keep left. But then comes the cut-scenes, including an interactive one battling The Boss. You have to respond to key prompts very quickly. Here they are:
- First sequence: LT (PSP) / L1 (PS3)
- Second sequence; LT, RT, RT (PSP) / L1, R1, R1 (PS3)
- Third sequence: LT, RT, Right (PSP) / L1, R1, Right (on the D-pad)
- Fourth sequence: Y (PSP), Triangle (PS3)
- Fifth Sequence ("The only thing we need to have loyality to... is the mission"): Left, RT (PSP) / Left, R1 (PS3)
The last two commands must be put in instantly. Do not wait for the prompts.
After many retries I completed it with 6:42 with 10/10 Cutscene Interaction Bonus. I am sure there is a little more flexibility as I had everyone's position memorized after the first ten tries or so.
This is easily the most annoying non-battle level when it comes to pursuing an S rank. It's much longer than all the others and is easy to screw up near the end. Be careful!
Next: Chrysalis Battle. Make sure that you've got the FIM-43 before attempting that mission.