Walkthrough: Ignore the fact that your weapons are holstered, because you won't encounter any monsters here. Instead watch out for radiation. Enter the nearest ventilation shaft #1 and after you've made your way to the train tracks head left. Eventually you'll find a large gate #2. Wait until you're let inside the base.
It shouldn't take long for you to get to the train platform #1. Choose a narrow passageway found to your right and proceed to the opposite end of this corridor. Check the ground near one of the barrels to find 3 rounds of gold ammunition #2.
You may now return to the metal gate you've passed by a few seconds ago #1. Head inside and continue moving to your right. Ignore a carriage with closed windows and instead search the area to the right to find 3 rounds of gold ammunition #2.
Retrace your steps to find a passageway leading to a new area of the base #1. You'll automatically trigger a cut-scene after entering a small room. Get ready, because as soon as you've been given back control over the main character you'll have to start running #2.
Remember to keep holding the SHIFT key. Follow your ally by choosing the same passageways as he does #1. Don't stop at nothing and ignore all enemy units encountered along the way. You'll soon enter a bar and you'll have to press the crouch key #2 to avoid getting shot. Maintain a crouching stance while trying to get out of the bar.
Stand up when it's safe and keep following your colleague. Notice that before you make a left turn you'll have a chance to collect 3 rounds of gold ammunition from a wooden crate found to your right #1. Bear in mind that it has to be done quickly so you won't get shot. Enter a new room. Notice that your ally has stopped #2. Head left here to avoid getting caught.
Use the stairs to get to the upper balconies #1 and keep heading forward. Don't worry after seeing a new cut-scene, because you can't avoid getting caught. You'll regain control in an entirely new area and you'll have a chance to talk to the Blacksmith. Exit the small room and proceed to your right to collect 3 rounds of gold ammunition from one of the crates #2.
You must now choose the only available passageway leading to the next area of the map #1. Walk through several corridors to end up in a bigger area #2. I would recommend that you take your time to purchase objects from the local merchants (one of them is selling supplies, two are selling guns and one is selling ammunition). In addition to that you can also buy two armors - a combat armor or a stealth armor (this one will come in handy in the next mission).
Approach several characters encountered in the area. Listen to what they have to say and use a ladder to find yourself standing in a small hole. Take your time to locate 3 rounds of gold ammunition hidden behind the ladder #1 and wait for a carriage to be pushed here #2. Pressing the action key will allow you to hide inside the carriage. Watch a longer cut-scene after which this mission will come to an end.