REWARDS - Respect
Head Downtown to the blip on the radar. Smoke heads inside the building and asks you to come in with guns blazing if he hears anything out of the ordinary. Something bad happens and CJ enters the building. You will see a life bar for Big Smoke, so make sure you are quick in taking out the enemies before Big Smoke dies. The pistol works fine in this scenario, so stick with that and autotarget the enemies and shoot them one by one.
After all of them are dead, run around to pick up the money and MP5s left on the ground. There is also body armor behind the one wall opposite the entrance you came in. When you're done in here, head towards Smoke and you'll go outside to some more shooting action. Once they're dead, you'll both hop onto a bike and Smoke will be controlling it.
This next part will have you firing like mad on motorcycles and cars that are chasing you. Don't worry about ammo since you'll have an infinite amount for this part. Also, don't worry about the big truck that chases you; there's no way for you to stop it, so just concentrate on the motorcycles and cars. You'll come upon a 3-car roadblock, so blast the middle one until it explodes and the other two will follow.
Smoke knows a way out of this mess by going through the flood control trench. Continue taking out the baddies until Smoke uses the truck as a ramp to get over the next roadblock. He points out that you need to blast the sewer cover on the right side in order to continue, so do so and Smoke goes through it. Blast the few tailing motorcycles, using the explosive barrels if you desire. Once you're through the tunnel, you and Smoke go separate ways for now, signaling the end of the mission.