Remark - game won't let you begin this mission until you don't destroy the Mobile Command Centre in the Downtown. Before you decide to begin it, you should upgrade your Smoke power, as it'll be very useful.
Get onto the roof in the central part of Downtown and confirm beginning of the mission. Game will display several longer cut scene with Hank and Reggie. When you regain control, you're in the western part of the district. Follow Hank, jumping onto next platforms. When you get to the big red pipe, wait until Hank blows it up and approach the place from where smoke is coming and activate this category of power. You can place yourself at the newly unlocked shaft and press Circle to change into smoke.
When you use the shaft, you're in the first part of the western island, which is a prison. Approach the first concrete column, pointed out by the game. You have to slide your finger on the touchpad, so Delsin and Hank destroy the support. You can move on.
From now on, you'll have to fight enemies. At the beginning, it'd be only the weakest DUP soldiers so you don't have to make any more complicated attacks. Move forward and destroy the second column as the first one.
Along your path to the third and the fourth column, you have to take into consideration that you'll meet enemies with superpowers, like an elite soldier with a minigun. You should focus on the latter one and remember not to get onto the verge of death or be pushed into the water. It's best to use the Cinder Missile (R1) to eliminate the more armored enemies, as you'll find smoke sources and heavy ammo on your way. Locate the remaining columns and destroy them (touchpad).
Make sure that you've eliminated all enemies and follow Hank. After a while an entrance to the shaft is unlocked. Press Circle after getting next to the shaft what catapults Delsin in the air and then land properly on the ledge above (you can turn into smoke to make that easier for you). Game will display important cut scene, from which you get to know that Hank betrayed Delsin. What is more, because of Augustine's intervention your character is totally helpless. You can't even use defensive powers.
When you regain control over Delsin, move away from the enemies who'll rush at you. Reggie will use a rocket launcher to eliminate them and if you stand too close, you may get hurt. Move up via the ramp and stand at the left cage. Behind rocks you can notice the first automatic cannon. Wait until it stops firing and then quickly run right (screen above). You may be slightly hurt.
When you pass the second empty cage, choose the left (higher) path. There is also a second automatic cannon here, so be careful. Move between next covers and place yourself in a way to be protected against its fire.
Stop at the bridge next to the cannon, wait for it to stop and then run to the other side. Quickly hide behind a good cover. When the situation calms, head right and then turn left (screen above). Walk into the huge arena and go left. After Delsin is stopped for a moment, wait for Reggie to move into action and approach your brother, after you free yourself.
After talk with Reggie, start helping him with freeing Eugene and Fetch. To do so, use the Smoke Shots on the concrete objects which are holding your allies. After releasing them, you'll another cut scene with a surprising final. It's not an end of the important things, as you proceed to first full encounter with Augustine.
Encounter with Brooke Augustine takes place on the big arena where you can move freely. As like in previous boss fights, try to keep Augustine at bay and don't get closer for melee attacks. Important is also to keep being mobile and/or hiding behind covers while Augustine throws things at you.
The best is to use the strongest Smoke Attack, which is Cinder Missile (R1), to attack Augustine. Notice that each hit destroy part of her cover.
Important thing about attacking your opponent is that you can't stop it for a longer period of time, as she will regenerate. So you should have a lot of heavy ammo (try to increase its limit with upgrades) and replenish it regularly. In this area you can find a lot of places to regenerate Smoke, but use them only when Augustine finishes her attack. Otherwise, your action may be interrupted (here an upgrade which decreases the time of draining the smoke may be handy).
When you destroy Augustine's cover, make some more attacks to hurt her directly. Fire until woman lands on the arena. In such a situation, you need to run up to Augustine and press the Triangle (if you play as the hero), or the square (if you are playing as the villain) to land a powerful kick (the above screenshot).
Further part of the first phase doesn't differ too much. You still have to destroy Augustine's shield and melee attack her only when she falls on the ground. After several sequences like that, game will let you to fire a special attack. You don't have to make anything special as this attack always hits. It means also that the second part of the encounter begins
Don't think that you'll be able to resume attacking Augustine at once, as she'll leave arena and send a group of soldiers at Delsin. Don't underestimate those enemies. Many of them have superpowers (and those should be dealt with as first ones) and many covers are already destroyed here. Don't stop for too long anywhere and don't let enemies get close to Delsin. Use the better attacks (rockets also) always when it's a chance to attack a stronger enemy or a group of them.
Augustine will join the battle after eliminating the main group of DUP soldiers. Notice that there are several new soldiers at the arena. You should get rid of them ASAP, because there'll be no more enemies. Augustine will move around the battlefield so pay even more attention to keep away from her.
Second phase of the encounter is very similar to the first one, so you again have to make strong distance attacks to destroy her shield. A difficulty may lay in a fact that you lose all places to regenerate Smoke, but, luckily, it doesn't weaken the main character. Why? Because now you can look for Vide regeneration points. Use the strongest power (Bloodthirsty Blades) which is as effective as rockets.
Continue attacking, using Smoke or Video whichever suits you. As in the first part of the encounter, after which series of hit, you have to kick Augustine when she lies on the ground (the Triangle or the Square). After several sequences like that, you may perform a special attack. Making it, ends this encounter.