This guide is going to assume that you are playing on the hardest difficulty available. The strategies provided should still apply.
After the opening cutscene the first chapter starts with you skiing. Pretty easy, just keep moving forward until you take your skiis off and pull your gun out. You'll see two enemies in front of you below a ledge that you start on. This is a good opportunity to practice getting good with your throwing knives. Throughout this campaign, you'll find several positions where you're faced with two enemies that are facing each other. You can easily use your throwing knives to take them both out. The first one won't move, and will die the second he's hit. The other guy will jerk back, and if you're aim is quick enough he's pretty easy to take out as well. Taking out enemies in pairs like this is a great way to progress quickly.
Then you can get some practice at another thing you should probably get used to. The guard towers. There aren't that many in this game, but it can make shooting from a distance problematic. These guys all have sniper rifles in their towers, and if they know you're there, they will shoot at you. The first guard tower you find will have four enemies below it, one enemy up top. Take your time, get a good idea of how the guy in the tower moves, and then try to kill him. If you got him, good. If not, don't worry. Just run for cover and try to get closer to him without exposing yourself.
The next four guys will be aware of your presence regardless. Two of them typically run for cover right below the tower, while the other two run towards the bridge. Don't be too agressive. Pick one off, run away. Rinse and repeat until the four of them are gone. Now go up into the guard tower, and pick up the sniper rifle. If you were able to take him out first, the rifle should have more ammo.
Now the game requires that you cross the bridge. You must move over this bridge. I tried to slowly make my way through the valley below it, but you'll just get blown up. Use the guard tower and look across the bridge to find the second guard tower. Pop the guy in there. This one is important. You need to kill this guy before he grabs his gun, because this one will have a lot of ammo if it remains untouched.
There's a small group of guards that will run around. Some of them will try to shoot you, and you might get hit. Thankfully they won't cross the bridge, so just keep picking them off until it's safe to cross. If you run out of sniper ammo, run on the under side of the bridge and have a close range weapon ready. If you sniped everyone, there will still be on guy towards the back of this area just a bit beyond the bridge. Don't worry about him for now, just stay out of sight.
There's a silenced pistol at the end of the bridge, pick it up and then go into the second guard tower. There's another rifle up here. It's not a one shot=one kill weapon but it's better than what you've got now. Go back down and stick to the left side of the building. Walk around and there will be a guy standing under a canopy. I'd recommend using a throwing knife on him to conserve ammo, but shooting him shouldn't attract the next group of enemies.
Move forward and you should get a checkpoint. This is where the game gives you some freedom. A vehicle will drive along the road to the bridge, stay up the hill to avoid being seen by it. You'll have some enemies behind you, ahead of you on the hill to the left is a group of buildings being patrolled by five guards. Follow along the road and you'll find two enemies talking to each other. You should use your throwing knives here, and sprint forward before someone on the hill sees you. I tried taking the hill, but doing so attracts the attention of the two road guards, everyone in the village, and the enemies that just came in behind you. Not to mention a guard tower that's too far ahead to kill the sniper in, or the fact that the hill patrol will use rockets and grenades on your position. I'd reccommend the hit and run option.
You'll get to the third guard tower at the compound wall, and this is kinda where I panicked and either got really lucky, or I'm just way better at this game than I initally thought. If you stick to the right on the cliffside, you can avoid being seen if you move quick enough. Move along the outside of the wall quietly, and you'll find a guy working on a gate to a tunnel that leads right into the compound. Assassinate him, and go inside the tunnel. You'll have a few more assassination opportunities, but then you'll be seen.
Once you're spotted, retreat to the tunnel. And then just camp this thing for a good bit. Enemies won't come in behind you the way you came in, so just keep facing the inside of the compund and kill whoever stands in front of you. There's an angle you can get at to where the enemies won't shoot at you while you pick them off. They will send reinforcements, along with a flamethrower, so make sure you've got enough firepower to take him down. Once there area is clear, and the initial alarm stops going off, slowly and quietly hug the right wall and keep going until you walk up some stairs. If you're spotted, book it.
Once up the stairs, go left, down, and then keep hugging the right. A path will lead you downwards, take it and you'll see a tree branch that goes over the canyon. Go across quickly but carefully, and then keep running until you find a small house. Run inside, and wait for enemies to stop searching for you. Exit the building, let your eyesight readjust, and then slowly go up the stairs. I died here, and respawned somewhere else entirely, but I had a new checkpoint and it seemed to be close to where I died.
After respawning, I stuck left and threw knives at the enemies I came across. I went inside the building where the character you're supposed to rescue is being held, and then someone found a dead body. The layout of this building is slightly confusing, but don't worry. No enemies are inside, so just sprint through. Head upstairs and work your way through the building. Once you reach the door, a cutscene will play.
After the cutscene, follow Astrid around until you have to hold your position. Move to the front left corner of this room next to a shelf, and slowly look out the window to take out the three enemies firing at you. Three more will come up after they're dead, kill them then get back to Astrid. She'll find what you're looking for, then you'll go downstairs. From here you'll be tasked with sabotaging two different points.
The first point is right out the front door, with a flamethrower standing at the entrance. Give him all you got, and take out the remaining enemies here. There are plenty of points to take cover at, so it shouldn't be too difficult. The second sabotage point is the same, but with no flamethrower. Once you've sabotaged both, get on your skiis with Up-Dpad and then go back to the bridge from earlier. Once you arrive a cutscene will play, and the first chapter is over.
The second chapter is without question the easiest chapter of the game so far. There are only two places that you actually have to fight people. The downside is that there is no real implication on which way you should be moving. Basically just keep running straight after the chapter starts. You'll come across a broken house with one guy standing at a fire. Assassinate him, then grab his gun. Warm up, move southwest to the hill, die if you have to and respawn. After respawnng move along the ouside of the hill, don't go up. The enemies here have no heat source, and there are a good number of them not worth fighing for ammo. After passing the hill, there will be three enemies here. Crouch toward the campfire and throw knives at the two guys here. Kill the third if necessary, warm up, move on. Stick left until you get near the end and then just keep running.
Another cutscene plays and then the third chapter starts afterwards. This third chapter is similar to the second chapter of Under No Flag, but slightly easier. You'll have three objectives. I'd recommend saving the farthest one for last, while the other two's order don't matter. There's a police station you'll have to infiltrate that's littered with enemies. Stay away and circle to the water facing side. Kill some of the dudes standing at the back entrance, rush in, camp some guys that might have followed you, complete the objective, then book it or die. Either one is acceptible.
The other object involves destroying a single truck. There are five or six enemies here that are mostly on their own and can be picked off with an assassination or a throwing knife. The last two are right at the truck. Shoot them and then pick up the dynamite nearby. It will be next to one of the guys who was standing still next to an ammo supply. Blow up the truck and move to the final objective.
You'll have to blow up some stuff in a sub, and then some stuff in a warehouse. Head to the sub first. More dynamite can be found nearby, only one is required to destroy the supplies here. Plant it, then jump off the sub and run under the dock to get a good distance away. If you're having trouble getting on the sub, there's a crane that extends over the sub that you can climb up to and jump off of. You can parkour your way over to the supply and assassinate an enemy guarding the stuff without being seen.
Stay under the docks, and move towards the warehouse, which is on top of more docks. There will be a guy down here, so be ready to kill him. There are also some stairs leading into this warehouse. Take them, kill the guys inside, blow up the supply, then go back down the stairs. There's a vehicle here that you can use to leave the area. Now you'll need to infiltrate a bunker.
The bunker is the part I found to be the most difficult, mostly just because of how inconsistent the enemy spawns were. You'll always have two guards at the bunker door, and two others patrolling. But there are random spawns that may or may not activate. It might spawn a sniper in the guard tower, or it could spawn him right next to the alarm tower. There's also a guy it could spawn below the guard tower, but his spawn was very inconsistent. Finally another guy could ocassionally spawn next to a vehicle to the right of the guard tower. Because of all the random elements here, it can be very hard to adapt and plan ahead. But basically, here should be your priorities.
1. The guy that might spawn below the guard tower - stealth kill
2. The sniper, in the tower or next to the alarm tower - stealth kill
3. The vehicle guard, usually spawns and next to a vehicle close to the two towers. - stealth kill
4. A guy who patrols slightly away from the bunker door. Always spawns. Watch his movements and either kill him quietly or loudly.
5. The alarm tower. This needs to be shot so either way the next enemies will be aware of your presence. Destroy this to prevent enemies from spawning in.
6. Door guard #1 and lookout. These two will start to move around after they're aware you're there. Just wait for them to pop up and take them out.
7. Door guard #2. This guy refused to move from the door, and his aim is ridiculously good for the gun he's holding. What's worse is he took about five sniper headshots to kill. Be wary of this guy. Be patient, keep hitting him, and keep a distance.
Move into the bunker and then a cutscene plays. Get on the vehicle, and a chase ensues. Just stay to the right and wait for the convoy to stop. This is the trickiest part of this whole mini-campaign. Stick left where a flamethrower will spawn. You want to run over this guy to kill him instantly. Cross over to the other side of the convoy wreck. You might get shot as you cross, and have to restart, but the other side has more weapons and more cover. Shoot the explosive barrels. All of them. Clean up any stragglers and then find the dynamite.
This final part took a lot of trial and error. Just be careful and kill the remaining enemies slowly. Once you blow up the last truck, be careful not to die. You don't get any more checkpoints. Just head to area it points you in. Once you arrive the last cutscene plays, and once it's over the achievement unlocks. Happy hunting!