Dead Space 3 walkthrough, Part Twenty-Two: Nexus Guts
Isaac now has the pieces to put together a Probe Gun to unearth the crazy secrets of the Nexus, a creature that will almost certainly not want its secrets unearthed. Is this a bad idea by Isaac and his team? Probably. Is it the only way to find the Machine that can shut down the Necromorph plague? Depressingly, it may be so…
Whether you want to complete the Protect the Armory Munitions Cache side quest or not, you can enter the Armory and find a Bench waiting for you where you can assemble the pieces you've obtained into a Probe Gun. If not, just make your way back to the room with the Nexus and you'll find a Bench. It's not a bad weapon in its own right, though it needs to cool down after four hits. Not good if you're being rushed by Necromorphs.
On your way back to the Warehouse with the Nexus you'll pass through the Barracks with the constantly-running film about quarantine. You may notice - and this is true for all areas, though you've probably never run across it before - that the Torque Bar door is locked again. Don't bother using another Torque Bar on this door if you've already gotten in once! There's nothing else of value left in here!
Outside the Barracks you'll begin running into more enemies. There are three possessed soldiers along the initial snowy path which will fire at you with little effectiveness. Get behind a crate and take them out at the legs, then blast the Necromorphic heads that detach before they can find new bodies. Eventually you'll see the shine of a grenade; this as a herald that a suicidal human is about to try to take you out with him. Shoot him quickly before he gets too close.
You'll be ambushed twice more on your way back. The first is on the drilling platform. Not too hard: circle and shoot. These Necromorphs aren't terribly fast and rely on close-quarters combat. The second is just outside the Warehouse, and it's a bit tougher - a combination of vomit-spitting Necromorphs and corpse-possessors. Focus on the spitters first, as they're much more dangerous, then take cover near the lift and blow away the soldiers by targeting their heads. This should prevent them for scuttling over to new bodies.
Once back in the Warehouse you receive some lovely info: you need to pry the thing's stomach open with harpoons. This is going to be disgusting. Run to both sides of the catwalks to activate the harpoons, using the cranks on the guns to pry open the ribcage. Norton will then usher you into a lift and set it in motion, lowering you into the Nexus' innards. Delightful!
You're looking to use the Probe Gun on the nerve clusters down here. (You'll know them when you see them.) The first cluster is to your right and down a short passage. Fire at it and you'll activate the Nexus' defence mechanism, a flurry of bitch-black Necromorphs! It's hard to see down here already, so aim for the eyes. These are no different than the fast, skinny ones you've encountered elsewhere. Don't allow yourself to be backed into a corner - they will gang up on you quickly. (This means sitting in the elevator itself is not a great idea.)
After the first wave is dead you'll need to find another cluster. Return to the elevator and go down the right tunnel; the cluster you want is attached to the ceiling, the middle of the three. Nothing will happen this time, thank god. The last is just a little ways down this tunnel, on the wall to your left. This one will spark something… very… different, at first, though in the end it just brings more Necromorphs. Plow through them and head back to the elevator.
Once topside, a long-expected betrayal will leave Isaac stranded inside the stupid cage. Use Kinesis on the control panel in the section next to the cage to get out (it's finicky, so mess around with it a few times) and head down the elevator. Now you have to save Ellie and the gang from a new threat: good 'ol Captain Norton.