You can think of this mission as a tutorial for the rest of the game. This mission will start by the game teaching you about jumping, stealth, camera system and character movement. When you are done with that make your way across the bridge.
There you will be greeted by the Empress’s daughter, Emily. She will ask to play a little game of hide and seek with you, if you agree to it, the game will use this activity to teach you a bit about stealth.
On your way to meet the empress you can chat with Anton Sokolov and Overseer Campbell but that is completely inconsequential. Upon meeting the Empress deliver her the letter.
After delivering the letter you go through a short combat tutorial. These enemies cannot be killed so do not worry about wounding them mortally if you are going for a no-kill play through.
The real mission begins when you have to escape Coldridge prison. This can be done in two ways either you can make a run for the exit or scavenge every last penny from the prison before leaving with no one even knowing about your escape until it’s too late. The latter way to get this done is also the harder one.
To get out of your cell take the key from the food tray and quickly go into the stealth mode. There will be three guards patrolling a small yard. The first of them can easily be sleeper held and his body hidden away.
Deal with the second guard when he is facing the prison cell and just as the third guard leaves him alone.
You can perform a takedown on the third guard when he returns.
However, if you do not want to give them any chance of detecting you, leave the two guards alone after you have dealt with first one and just continue your path by slipping past them around corners or when their backs are turned towards you.
Follow the path ahead and it will lead you to a guard who has the key for the interrogation room door. Pickpocket it off him or just choke him out and then take it from him.
When you are in the interrogation room take the explosives from the safe and go back outside. There will be two guards patrolling the maintenance yard. Taking them out is advisable as this will assure you can come back to this yard without any worries when challenging the next area.
The prison gate is divided into two parts. The first part is covered by three guards. One in each of the two booths and one outside. The second section of the gate has two guards you need to worry about. The first of the guards is in front of the security doorway at the foot of the stairs. The second is at the top of the stairs.
To get past the first set of guards is easy. Just mantle onto the ventilation pipes above to get over the heavy security door. Choke out the two guards in the second section of the gate. If you do not do this, they will surely see Corvo when he blows the door up later.
After setting up the explosives crawl into the metal container near the door. By hiding here you will be close enough to the escape route and at the same time protected from the explosion that is about to happen.
When the fragments of the door are sky-high wait until all the guards have returned to their positions and then step outside to dive down into the water. You will find the sewer entrance directly across from the broken stairs where you exit the prison from.
The only foes you will find in the sewers are the stinking rats for a while. Killing them does not affect your Clean Hands and Ghost achievements.
Do not let the rats gang up on you though, they can kill you if that happens. You will find a valve wheel that is blocked by a dead body. Move the corpse out of the way and turn the wheel.
To turn the next wheel you need to distract the pack of rats surrounding it. Take one of the corpses dropped in the sewers and throw it as a lure for the rats. With the rats interested in something else go on and turn the valve to open the exit.
Once you are in the chamber with the chain hanging in it. Climb all the way to the top of the chain and jump to safety. Corvo is equipment is not far off now, but first you have to deal with some crossbow traps.
One trap is the near the foot of the stairs. Second one is the near the off-shoot with some valuable items. Disarm these traps by going near them and when you have done that, you can trip the trap wire without any consequences.
You will locate Corvo’s gear in a traveling trunk. The trunk contains his armor, crossbow and incendiary bolts.
There are only four guards when you drop down to the final section of the sewers. However, if you had alerted anyone before that to your presence, there may be more guards waiting. After dealing with first guard you can go past the next three guards through two ways.
Either you can dive underwater and swim to the exit or travel upon the pipes over ground to avoid detection. Interact with Sam the boatman outside to effectively end this mission.