Stronghold Catacombs is a Syphon Filter mission where Gabe must find Jonathan Phagan and Lian Xing.
Part one: As the mission starts, you will se a guard in front of you. Eliminate him and climb down to where he was. Look to your right: there is a box with a silenced 9mm if you need ammo. Then go left and climb down the stairs, fallowing the scientist. Always remember to keep a reasonnable distance between you and him. When you get to the bottom of the stairs, take cover in the alcove on other side of the tunnel. Soon, you will see a guard passing by you. Eliminate him quickly. Keep going after the scientist.
The scientist will pass between two guards, standing on each side of the tunnel and facing each other. Just before them is a crossing. Crouch so your steps won't make noise, and turn right. Take your left at the next crossing. There will be a guard walking ahead in the same direction as you. Eliminate him and you might also see another guard further ahead. You can just ignore this last one. Turn left at the next crossing.
++++++++++++++++++++++++++++ + Hint: Alternate strategy + ++++++++++++++++++++++++++++ It is possible to take out the two guards facing each other by throwing a gas grenade between them. You must really in the middle of the tunnel, so that the cloud of gas will reach both of them. Keep going straight ahead and you will end up in a room with stairs in the middle. The scientist will be on your left.
Back to main guide ~~~~~~~~~~~~~~~~~~ Keep fallowing the scientist, but after he is passed the corner on your right, stay hidden in the tunnel where you are. A guard will pass before you. Take him out and after that you will be able to pass the corner too. Fallow the scientist to Phagan's cell and there will be a cutscence (objective completed/ checkpoint). Part two: You must now follow Phagan to Lian's cell. He is unarmed, so you must provide cover fire for him at all time. In general, you should stay close to him to that you draw enemy fire on you. Stay on your guards because you will often be surrounded by enemies. You will frequently be attacked from behind after one or two guards have pulled your attention in front of you. Always eliminate the threats closer to Phagan first. You should also ignore enemies that are not directly in
your way. Thus, if you let Phagan take to much lead on you, he is most likely to get killed before you know it. A few enemies are equiped with flak jackets, so headshots will always be a winning strategy. You will get one checkpoint on the way, when you come to a larger room with stairs in the middle of it. When you reach Lian's cell, there will be a cutscene (objective completed/checkpoint).
Part three: This time, Lian and you must find the exit to the catacombs. Lian will lead the way. Unlike Phagan, she is armed with a .45. Still, don't let her do all the work, she is not that efficient. However, it means that you can not more easily deal with enemies attacking from behind while Lian keeps the ones in front busy. Again, the faster you deal with the enemies, the greater your chances are of making it out alive. Always give a hand to Lian and never leave her alone for too long. You will also get one checkpoint on the way, after you've climbed down some stairs. You will eventually get back to the very place where you started the level. There will be a few enemies wearing flak jackets waiting for you. Take them out and follow Lian to the exit (objective completed).