Chase the traitor
To start with, go down the two flights of stairs and turn right. Follow this corridor to another set of stairs. As you descend these stairs, make another right. You will see Mitchell slamming a gate in front of you. Press twice to bust through the gate. You will find yourself in a big open section next. Be warned, there are hostiles in this area. Ignore the first two hostiles and concentrate on the one blocking your way. You can also eliminate all three of them, but you have to be quick about it or Mitchell will get away.
Once you have cleared the area, smash to the wooden gate blocking your way. Run to the end of this corridor and make a left. You will see Mitchell on the other end of the corridor, running through an opening. Be warned, he will slam the gate in that section. Turn right at the opening and drop down. You will see a low barricade in front of you. Vault over the barricade using , and continue on. At the end of this section, you will see a wooden barricade to your left. Press to bust through it. Continue on down this path, taking a left at the end. You will notice a low wall at the far end. Vault over this wall, and turn right. There is a blocked door in front of you. Bust through it using . Once you have regained control, continue on this path, turning right at the end of it. If you roll fast enough, you can avoid the falling debris in front of you and continue on; if not, run forward an vault over it. Run forward and climb the ladder to complete the underground section
This next part can be a bit of a headache. You are above ground now. Follow Mitchell, and he will lead you to a big area with a fountain in the middle of it. There are hostiles in this area, including one carrying a Hutchinson A4. Using the fountain as cover, and eliminate the hostiles. Now, this next part is very important. When you go into the opening on the other side, at the end, to the right, there is a door. Now, the door is a checkpoint. If it does not show up as a checkpoint, pause it and save from the last checkpoint. You are going to have to restart the level or your system. Now, if it does show up as a checkpoint, go through the door.
Prevent the car from escaping
Mitchell has gotten into a car and is getting away. What you have to do is go into the ultra aim, and shoot both tires. Once you have done this, a cutscene will ensue showing Mitchell getting thrown from the car.
Once you have control of Bond, run up the road. You will be interrupted by a cutscene showing a van running into another car, and three bad guys jumping out. Once you have dispatched of these three, take the stairs to your left. At the top of the steps, to your right, there are various nefarious characters who are looking to end your game. Use the Hutchinson A4 (shotgun) and using the corners as cover. The machine gun will do it as well, but the shotgun has more power. Once everyone is gone, take the steps to your right. They are in an alcove. Run to the top of them and turn right.
Follow the balcony along, vaulting over things as necessary until you reach a door with two dryers to the right of it. Be warned, there is a gunman in the tower to your left. There is also one ahead and above you, and two more gunmen to the left at ground level. Once they have been dealt with, climb the pipe in front of you. To your left you will see scaffolding. Follow the scaffolding til you drop down a level.
Tanner can not believe Bond just did that. Once you have shaken the cobwebs out, step out of that door, and use the wall for cover. There are two hostiles lying in wait for you. One of them is carrying a Hutchinson A4. Once you have dealt with these two individuals. Run to the door, and climb up the pipe.
Fight the traitor in the dome
Once you have control of Bond, start to move to the right, using the wall as cover. You will notice that Mitchell moves right along with you. Now, this is important, you are going to have to deal with the hostiles above you as well, so be ready. Now, there are three "traps" that you are going to want to guide Mitchell to. From where you start, the first trap that he will be under is a board hanging from a scaffolding. Shoot at it. Once you have done this, move on to the next one, remembering to watch out from above. The next trap as you continue right is a scaffolding with boxes on it. Shoot at it when Mitchell is underneath it. Move along to the final trap, which is a scaffolding with a bunch of pipes. Fire at it to get to the next part.
The next part consists of quicktime events, or "button battles." They are completely randomized, so just try to press them correctly as they come up. If you haven't finished the level and the Dimitrios fight, try placing the controller on some level surface and be ready to hit those buttons using both of your hands.