While in the sewers and tunnels, be prepared to shoot a few rats and cops. Or you could just double-click to run away; the choice, as they say, is yours. From the bottom of the street entrance stairs, go left and cross the tunnel. Click on the electric chair. Go through the broken north door from the electric chair. Down on the crossway, throw the lever to extend a walkway and go to the right. You might see Lucy (if Steele didnt shoot her). Give her the VK to see what she really is...
If you didnt buy special ammo from Bob, go left to the weapons cache and click on the crates twice to get some. Go right and up screen to the crossway and go to the lower left. Continue down the stairs and go left to the manhole at the apartment.
Go up and enter your apartment to talk to someone. This step was necessary to thin out the cops in the tunnels near door 5. There may still be an occasional cop, though. Go back to the crossway in the sewers and go left through the large circular opening.
Turn right and take the big elevator down. With your dialogue set to the question mark, choose the following as you talk to the drunk... OTHERS, FAT MAN, then click him again. He wants some booze, which is a nice thought in anyones book. Go to the crossway and straight across to the weapons cache and climb to the street.
Get a flask of wine at the China Bar and return over the crossway and on to the drunk. First ask him about the sewers, then give him the wine. Then ask him all you can before he passes out. The lightweight. Take a look through the iron gate at the top of the short stairs on the left. Go past the elevator and take the right tunnel to the plank and SAVE! Start across the plank. When the rat appears, return to the left end of the plank, draw your gun and shoot the rat. If you previously selected the high power ammo, one good shot will do.
Cross the plank and make sure your dialogue is set to the question mark. If the twins arent there, click the lower left monitor to download the Luther/Lance DNA. Leave and return to the room several times until the twins show up. Talk to them, with all choices from top to bottom, until they ask for Tyrells DNA files. Then quickly save your game. From the twins, exit the door under the light, climb the tall ladder and climb the short ladder and quickly enter the elevator behind the guard. Get the DNA from the table.
The previous directions to Tyrells office are for playing in easy mode (unlimited cash and ammo.) The following is an alternate route to Tyrells office... Return to the crossway and go screen left toward the room before the manhole. Go through the northern door and go north. This route is probably locked until you have to follow it to the moon bus in Act 5.
Sneak back into the sewers and give the DNA to the twins. If they are not there, and you havent previously done so, click the lower left monitor to download the Luther/Lance DNA. Leave and return to the room several times until the twins show up. They give you the whole scoop on things. Go up the steps behind the twins and call Guzza on the console. Behind the clown, go down. If the twins arent there, do a download of the small left screen behind the twins chairs, if you havent already done this.
Go back to the drunk and save. Go through the iron gate and talk to Guzza. When you have the chance, you can either run away (suggested) or just shoot Guzza. If you shoot him, the Reps tell you to go to the moon bus. If you decide to run away, move as far left as you can when Clovis is talking to Guzza. When you have the left blue arrow, RUN! Either way, you have to return to your apartment for Act 4 to end.
To return to the apartment building, leave the platform and take the elevator up. Return to the crossway and go screen left to the manhole and enter the apartment building. Theres a long movie and Act 5 starts.