This is one of the harder quests in the game. Highly recommended to complete some optional quests first to level up.
Although you can do this quest without using your Invisibility, it is a bit harder (You have to fight about 6 more enemies). Getting a Meditation Pill beforehand is recommended.
It is also recommended that you purchase a gun and some ammo as well as some Energy Drinks before you go, just in case. However, if you don't want to spend the money, you can just equip the kitchen knife and then equip the sword you get later, and you should be fine.
When you're ready, click on the Black Car in front of the Hospital and head over to Area 69.
When you get there, take your Meditation Pill and turn invisible.
Go over to Building A.
When you enter the building, you'll see two Henchmen guarding a door. Go through the door and listen to their conversation.
The next room is empty save for a Vending Machine selling Cuma Colas. Come back here as often as you need to heal yourself.
If you go straight through the next door, you'll see two towers with blue lasers in between. You need to find two keycards, one for each of the towers, to unlock the door. If you pass through the lasers, you will turn visible again.
Go to the left, walk pass the two Henchmen, and go left again.
In this room, there will be two henchmen with goggles that allow them to see you. Kill both of them, and then go through the little whole in the top wall for a cool Easter Egg.
Go back to the room where you killed the two Goggle-henchmen, then go right to the room with the two normal Henchmen. Go down from there.
Search the cabinets in the top left of the room to find some Ammo.
Go down again to find a Scientist working by himself. You speak to him and then have to choose whether to kill him or spare his life.
If you kill him, he dies quickly. Your Morality decreases by 5.
If you spare him, he runs off into the other room and brings two Goggle-henchmen to attack you. Morality increases by 5.
Either way, after you deal with the Scientist, search the gray box by his console to find an Energy Drink and an Orange Keycard.
Go back up, and then right and you should be back in the room with the Vending Machine. Restock if you need to.
Go up again and click on the Orange Tower (the left one) to unlock it with the Orange Keycard.
Go right now, and search the box in the room to find another Energy Drink.
Go right again and kill the single Goggle-henchman.
Go right again and search the leftmost box to find another Energy Drink.
Go back left one room and then down.
Go right and kill the two Goggle-henchman.
Go right again and encounter the creepiest, sexiest girl you've ever seen. At least you know what the key that you found in your basement goes to now. You have to return later to enter.
Go right again and you'll find another Scientist, although this one is jerking off. Search him and you'll find the Blue Keycard in his pocket, but when you grab it you get his jizz on your hand. Nasty.
Go back left, into the creepy door room, then go left again. Go down, kill the Goggle-henchman, then go right and search all the boxes to find a Cuma Cola, an Energy Drink, and some Ammo.
Go back the way you came and return to the room with the two Towers and the lasers. Be sure not to cross any lasers on the way there.
Use the Blue Keycard on the Blue Tower.
Go through the lasers and into the now unlocked door. You'll become visible again.
Search the Green Filing Cabinets to find the documents that Betty is looking for.
Exit the building by going down, past the lasers, down, past the Vending Machine, down again. You'll have to fight the two Henchmen at the door because you're visible now.
Exit the building and go back to the Black Car and return to the Hospital.