The survival fun never ends in ZombiU, and this time yet another party wants you to help them out: a small girl who claims to be trapped in St. George's Church. Prepper warns you against going to help her, but you never really listen to him anyway.
Leave the Safe House and head for the lobby of the subway station. There may be a zombie or two lurking down here, so kill them off, then scan-hack the door near the rubble. Inside you'll find Planks and Handgun Ammo sitting on the floor. Per standard procedure by now, follow the path until you find an Exit door. Continue past here until you find a tunnel full of water.
Walk lightly - two zombies will rise up here and come at you. Kill them, then look around for a Mine and Handgun Ammo. A bit further on two more zombies will come at you - same deal. Be careful past here, as there's an active mine on the floor, just before the stairs out of the water. Shoot it, then keep going. Two MORE zombies will show up, one crawling. Easier than the last two.
Check the side for a crawl space. Inside are Handgun Ammo and C4. Remove the bar from the door and go through. Head back to the crawl space and instead push the ruined lockers to the side. Go up and into the next room to find a zombie to waste, then crawl through another wall. Go through this tunnel and into an adjacent tunnel.
You're now in a tunnel so dark your light can't see the end. Check the side door first - it contains a bunch of dead guys in chairs, one of which (closest to the door) will go for you. Take off his head. The only thing in the room is Chocolate, so you may want to skip the encounter. Head out, into the hallway again, and edge around the corner at the end.
There are a bunch of zombies in the hallways nearby, though you can't see them very well. Once you catch one in your flashlight, use a Flare and Molotov combo to take them out. Beat off the SWAT zombie that remains and keep going. Pick up the Large Medipack at the end of the hall, then unlock the door beside you and go in. There are Planks in both halves of the room, a code you can't yet decipher in the first half, and two zombies to kill in the second, one crawling and one in a chair at first. There's also a code door, but you can't open it with your current technology.
Keep going down the main hallway. You'll find two doors, one at either end, and a debris spot you can blow up. One of the doors is being persistently knocked at, but the zombies can't seem to get through, so start with the C4 spot. It leads into a bathroom. Go into the back of it and get rid of the zombie hiding there, grab the Upgrade from the floor, then check the stalls for Handgun Bullets. That's all for this place.
Next is the door across from the bathroom. Something has been blocking your radar again, and it's in here. Take out the little dish in the corner - but first, have a quick look around the room. There's an exploding zombie here, and it will end your visit real fast if you're not alert.
Check the side of the room to find a vent. Go through it and, after crawling a few paces, you'll see a split in the path - and one of them has a house symbol. Use it to get back to your Safe House via a manhole, save, and return to the vents.
Going left from here is useless, so crawl past the body and drop down onto the board in the next room. You're now standing above a series of stone passageways filled with zombies, and you need to carefully make your way across the top. Move slowly, and when zombies on your level come at you, either whack or shove them off the walkway. It's much easier than it looks, as either will usually send a zombie off the edge with a single go. Crouch through the space at the end.
There is Carbine Ammo in the room ahead. Grab it, then look through the archway. You'll see a spitter to your right, and one, possibly two more in the doorway at the far end of the room. Kill them here, as they'll lob acid at you while you try to cross this next room otherwise. Once they're gone, backtrack to your first right and go across the narrow beam. In the next room you'll have to keep doing the same; just keep your eyes on your toes. Don't worry about zombies coming to life near here - they will just drop off the edge and into the water below. Calm, methodical steps are vital to not falling.
Go up the ladder on the opposite side. At the top you'll see an exploding zombie; shoot it quick to kill it and possibly the normal zombie nearby. Head into the room and check for a Large Medipack in the back, then go through the wall on the left side of the hallway. Unbar the door in here to find an easy way back into the sewers, then go up the ladder. You'll be treated to a quick cut scene -
- and get knocked out. By humans. Yep, it was a trap.
The next part of the game is harder than anything you've faced, and harder than anything you will face. Before going up the ladder you may want to brush up on your zombie-slaying skills with the absolute basic weaponry at your disposal - you'll need to minimize your item usage for the task ahead.