As the chapter begins, follow Dr. Jimenez forward and through the gap in the brick wall. Go through the closed door with blood on it to the right. Interact with the mirror to temporarily return to the hospital and purchase some upgrades.
Once you're in your hospital bed, leave your room and turn right, following the hall through the reception area and an iron gate. Sit in the chair to purchase your upgrades, and when you're done, go to the opposite side of the hallway (left when you leave your room) and once again interact with the mirror. This will return you to the chapter and Dr. Jimenez.
Exit this small shack and turn right, going in the nearby door to do some minor looting. Dr. Jimenez will spot his brother, Valerio, who appears to be working on a patient. Things get ugly upon closer inspection, and when you regain control, you'll want to immediately put four rounds from your Handgun into his head. You could use the Shotgun if you prefer, but he drops easily enough either way.
With the big guy down, head into the room where he was conducting business and start interacting with the body on the table. It might take some work, but eventually you'll dig out a key the patient appears to have swallowed.
Spend a few moments checking out the upstairs, then backtrack out of the house and head to the street. You'll want to turn to your left and move up to where a cart is parked along the left shoulder, then turn into the walkway just before it. Kick the door down and head into the next room, moving down the two flights of stairs and into the hallway. Be sure to dip into the door on the left and grab some supplies, then get back to the hall and continue moving forward.
Go through the door at the end of the corridor to find Leslie in the back room. You'll also be attacked, but it's nothing your Shotgun can’t fix. When the coast is clear, backtrack the way you came to trigger a cut scene. At its conclusion, Ruvik will be walking away from you. It may sound silly, but do your best to follow, eventually triggering another short cut scene.
We're not sure what happened, but you're sitting in a basement full of blood and guts. Since there isn't a good reason to sit in this crud, climb up onto the catwalk and crawl forward to sneak under the nearby trap. When you approach the door, you'll get another brief look at Ruvik, then it's time to fight a hefty batch of random creatures.
Tip: Lure the creatures through the traps in the area for easy kills, or look for a side room that has some explosive red barrels inside. Wait for the creatures to follow you in, then shoot the barrels to kill several of them in one go.
Whatever method of destruction you decide to go with to clear out the creatures, when the last one is down, you'll see the door that Ruvik was standing near open. Spend a few moments going through the area, burning bodies and picking up whatever goodies they may have dropped, including the Shock Bolt. When you're ready to move on, head through the door where Ruvik previously appeared.
Follow the corridor in the only direction you can, moving into the next room and forward until a giant Spider attacks you. Don't bother trying to fight it, just run back down the corridor and hang out by the white door. When the Spider gets close the door will open, which is your cue to get the heck out of there. Just keep following the only path you can until you reach a room with a ladder.
Tip: The room with the ladder has a button beside the door. Press it to close a gate, buying you a few precious seconds to loot up before making your escape.
When the room is adequately looted (or you're out of time), head down the ladder and keep moving through the hallway. Make sure to duck under the traps, then sprint into the elevator to catch your breath. The ride won't last long, and when it's over, you need to get off the elevator in a big hurry.
As you might expect, the giant Spider of death is back, so just sprint forward and through the door on your left, then keep moving as quickly as you can to dive under the door before it shuts you out. When you regain control, you'll be on some large metal stairs. Descend these stairs until you see Ruvik, then head back up to trigger the chapter ending cut scene.
Continue with The Evil Within - Chapter 5 - Inner Recesses.