Complete mission walkthrough:
We'll start off with a short cut-scene (#1). You won't have to read all of these dialogs. Sadly, you won't be allowed to skip the cut-scene, so be patient. You'll start inside a small cell. Your main objective for this first mission will be to escape from the fortress. Exit the cell and destroy the first barrel (#2). You'll find your first crab pendant inside. Pick it up. Head on to your right. Destroy the second barrel. You'll probably find a medkit inside. Take it, as you may need it later during the game. As for the rest of the barrels, you will find gold inside most of them, however it's going to be random whether you find something or not. Use the stairs to reach the lower level.
Once you're at the lower level, you might want to consider destroying some of the nearby barrels and crates. You should be able to find a health pack inside a crate located to your left (#1). As for the other barrels, some of them will contain gold pouches. Head on to the prisoners and talk to them (#2). Get ready for your first fight!
You shouldn't have any major problems killing two enemy thugs (#1). I would recommend choosing faster attacks, especially in the early part of this fight. Alternatively, you could try and score some kills for one of the sub-missions. You would have to trick enemy units by standing near the pit (#2) and performing a dodge maneuver. Either way, they have to die.
Once the enemy units are gone, you must go back to the prisoners. Jack should automatically free them. Once this is done, head on to the left side of the room. Stand on the glowing spot and press the action key (#1). As a result, you are going to be transported to a new location. Once you're on a new level, head on to your right. You won't find any crates or barrels in this area. Talk to one of the prisoners (#2) and use the handle to free him and his colleague. You will have to find two more cages to fulfill one of the subquests.
Head on to your left. You should be able to find a second glowing point here (#1). Use it by pressing the action key. Don't worry about one of the thugs, because he's going to be attacked automatically. Once you're on this ledge, you'll face-off against your first miniboss. Thankfully, this is a very easy fight. The game will suggest that you block most of his attacks (#2).
You will have to wait for the right moment to perform a successful counter-attack (#1). I would recommend that you focus on faster attacks. You should be able to hit the miniboss at least three times before having to use the block feature. This fight will probably take only take 30-40 seconds (#2). Once it's over, head on to your right.
You should be able to spot a third cage here (#1). Go there now. Once again, you will have to start off by talking to the prisoner. This time you will find out about the secret locker. We'll get back to this problem later during the mission. Pull the lever in order to free him. You will also come across a few crates here. Destroy these objects. Use the ladder (#2) in order to get down to the lower level of the complex.
Head on to a nearby staircase. You will probably notice a small door along the way. The door is being guarded by a single enemy unit (#1). Take care of this small problem. Now, that the area is clear, use the lever, so you'll be able to enter this new room. Sadly, you won't find any barrels or crates inside. Instead, head on to a glowing dot. You will have to press an action key here (#2).