The mission begins with Vaas defining what insanity is, then pushing a large rock which you're tied to into the cenote. When you see a button on the screen, mash it to break free of the restraints, then swim to the surface. Go towards the objective, but crouch when you get there, as there's a guard standing on the other side of the waterfall. Use a Takedown on him, then grab his weapon since Vaas didn't leave you with anything.
Sneak up to the next two enemies, taking them down and grabbing their weapons. You can either take the road that leads into the camp, or go up on the ridge and use your camera to scout the area (recommended). You'll see a helicopter pass by, which is going to be your objective here. If you die at all, then you will have to restart from where you landed in the cenote.
There is a sniper and a RPG on top of the buildings, then at least 3 normal enemies walking around. If you get spotted and the enemies sound the alarm, then a timer of 5 minutes appears, so stealth might be a priority here until you can disable the alarms. If you have the Death From Below skill, sneak up to the nearest building and use it to take down the sniper there.
From here, take out the enemy at the far end from where you entered, then head back to the ledge and do a Death From Above takedown on the enemy that walks by. Sneak over to the other building and do a Death From Below kill on the guy with the RPG, then sneak behind the last enemy in the area to kill him. Once they're all dead, head over to the alarm and disable it.
With the alarm disabled, head to the bridge, but don't cross it. Go in the water and slowly creep up onto land and forward until you can spot some enemies with your camera. There's a mounted machine gun on the building closest to you, as well as two snipers on the buildings on the far side. In addition, there's a dog to the area left of the chopper, and three normal enemies on the ground.
It's hard to take out all of the enemies without being noticed, so just run in and start shooting the ground enemies first. If you picked up the sniper rifle from the one enemy in the first area, use it to take out the other snipers. Once all of the men are dead, head to the chopper and get inside.
You'll force the pilot to take off, but before you get too far, a guy with a RPG will show up and shoot the chopper down. A cutscene will occur where Vaas will walk up to you and shoot you in the chest. You'll wake up in a pile of corpses, and you'll need to do some quick time events to escape. It turns out that the lighter Vaas put in your pocket during <> is what saved you.
You now need to get your stuff back from the pirates, so turn around and head towards the marker. You do not have anything at all, even your camera, although you seem to have the items in your rucksack. There's a Radio Tower very close by, so if you haven't activated it, you might want to wait until you get your stuff back first.
It's best to approach the camp from the hill, as you can sneak up behind the enemy by the fire and drag his body behind the building. Do the same with the next one, then sneak into the building in the middle of the camp. Takedown the guy with the Molotov, then go near the road and kill the guy sitting in the chair. There should be a C4 in one of the buildings, so grab it before heading to the final building.
All that is left are two dogs and a Heavy Gunner inside the far building. As you get close to the building, you'll hear your phone ringing and driving the guard nuts. You'll likely be found out by the dogs, so slash them twice to kill each one. Throw the C4 by the doorway and when the Heavy Gunner is close enough, detonate it to take him out. Go inside and grab your stuff from the cabinet, which will end this mission. It's best to go and activate the Radio Tower nearby if you haven't yet.
