After finding the plugs and completing the extremely long Sewers section, you will reach the NEST Laboratory. Continue forward until the door opens, then enter through the door on the eastern side to leave your partner somewhere safe and begin exploring the facility. (If you are playing as Leon, Ada will remain in the cable car.)
Beside the bed, you will find a computer where you can read [IMPORTANT] NEST-wide Alert. In the same room, you will also find the Research Lab North Area Map and some Flame Rounds/Shotgun Shells on the counter.
Now head out to Reception. There is a computer on the counter displaying the Nap Room Log. The small adjoining room is a safe area, and you can find the ID Wristbands file on the whiteboard. Leave Reception through the eastern door, the only one currently open.
We are going to enter the Cafeteria, but be careful because there are four zombies inside. You can collect a Hand Grenade from the lower-right corner and some Needle Cartridges/Fuel from the left. Now climb the ladder at the back of the room to reach the Kitchen.
As soon as you drop from the vent, you will find a container of Large Gunpowder to your left. A little farther ahead, there is a Combat Knife. Carefully open the door, as there is a zombie beside it. Eliminate it, then open the door leading to the Nap Room.
On the desk, you will find some Flame Rounds/Shotgun Shells. Inside a locker is the High-Voltage Condenser (Spark Shot)/Regulator (Flamethrower). Take the Upgrade Chip from the hand hanging out of one of the pods and combine it with your ID Wristband.
You can now open the door leading to the Cafeteria hallway, return to Reception, and go through the southern door.
As soon as you go through the door, you will see the body of a U.S.S. soldier slumped against the railing. Collect the Special Forces Recording from the body. Press the button beside the bridge to deploy it and cross to the other side. Once you reach the central platform, your only option is to head south and activate the bridge leading to the East Area, your next destination.
The Lobby is a safe area where you will find some Gunpowder and a Green Herb. Now leave through the eastern door. Examine the glass: it contains what you need, but... well, leave through the northwestern door. Do not panic in the hallway. Continue forward a little and you will see a "thing" hanging from above. This is a new type of enemy.
It is an "Ivy Zombie," and its most vulnerable points are the yellowish bulbs covering its body. If you manage to destroy all of them, it will immediately collapse to the floor. If you have trouble dealing with it, return to the glass-walled room. It will lose track of you, allowing you to catch it by surprise again.
Once the room is clear, collect the High-Grade Gunpowder (White) from a small table near where the creature was hanging and continue. A little farther ahead, you will encounter another carnivorous geranium. Eliminate it and enter the Greenhouse Control Room.
Interact with the machine beside the glass to trigger a cutscene and obtain the Dispersal Cartridge. Before entering the Greenhouse, examine the panel on the northern wall and enter the following codes:
Note: The Greenhouse puzzle codes are different during a 2nd Run. You can find the alternate codes at the previous link.
Now enter the Greenhouse. There is a Red Herb and a Blue Herb, but bear in mind that Ivy Zombies will continue to appear. You do not want to remain here for long. Head northeast to the Drug Testing Lab. There is another container of Large Gunpowder on the table in the center of the room. At one end of the same table, you will find the Herbicide Synthesis file.
Since you entered the codes shown above in the Control Room, you can now interact with the machine in the corner. Insert the Dispersal Cartridge (Empty) to begin another puzzle.
Since you may have already moved something, which would make a simple sequence of button presses useless, here is what you need to do to solve the puzzle:
Note: The herbicide tube puzzle is different during a 2nd Run. You can find the alternate solution at the previous link.
Return to the Greenhouse. Since you entered the codes shown earlier, you can now climb down the ladder in the southeastern corner. Once you reach the basement, inspect the opposite side of the room before heading toward the door to find the Research Lab East Area Map and another container of Large Gunpowder.
Go through the door and head south toward the Lounge. You will find some Flame Rounds on a bench and a Trophy on the central table. The Trophy is no longer useful, as it merely reveals the solution to a puzzle you have already completed. Continue west without running.
At a certain point, two Lickers will drop from the ceiling beside the western door. If you are walking, they will not hear you, allowing you to move into the corner and take aim before blowing their brains out. Be careful, as the zombies beside the vending machines have also gotten back up.
Once the area is clear, head west and climb the stairs. There is a zombie at the foot of the stairs, another will fall on top of you while you are climbing, and a third will emerge from the back of the room when you reach the top. After eliminating the third zombie, inspect the room. There is some High-Grade Gunpowder (White) beside the door you entered through.
You will also find some Handgun Ammo inside the lockers on the left. Beside the circuit breaker on the wall are Somebody’s Note and the Signal Modulator you need to continue. You can use this device to interact with the circuit breakers you saw in the Nap Room and Lounge. We will begin with the Nap Room.
When you reach the room, notice that the circuit breaker has a frequency: OSS, MURF, AWS... Examine the Signal Modulator, set it to the correct frequency, and turn the dials until the waveform is aligned. Once this is done, close the menu and use the modulator on the circuit breaker. To make things easier, here are the solutions:
Restoring the power will open the Nap Room pods. A zombie will emerge, but if you are quick, you can collect the Hip Pouch and read Wayne Li’s Note before getting the hell out of there. Now return to B2 and repeat the process with the circuit breaker in the Lounge.
Activating the Lounge circuit breaker will open the door to the Server Room to the north, which is a safe area. Enter and collect a Combat Knife, some High-Grade Gunpowder (White), and some Flame Rounds/Fuel. Now head southwest to the Low-Temp Testing Lab.
This is not your first rodeo: that zombie slumped against the wall is a threat, so eliminate it. You can inspect the computer to read Wayne Li’s Inbox. Then enter the frozen room on the right. There is some Gunpowder and a machine where you can insert the Dispersal Cartridge to obtain the herbicide.
You now need to climb the stairs and return to the Greenhouse Control Room. Alternatively, you can go directly up the stairs leading to the area with the plant and then continue to the Control Room. The choice is yours.
Use the herbicide in the machine in front of the window to destroy the plants in the Greenhouse and watch as the corpse carrying the chip you need falls to the ground.
Enter the Greenhouse, head to its southern end, and then continue west until you reach the corpse. Collect the Upgrade Chip and combine it with your ID Wristband. Now run back to the Control Room, because the Ivy Zombies will get back up and there is no point wasting ammunition on them.
Before continuing, you can now use the computer in the Conference Room to read Byron Cartwright’s Inbox. Return to the central bridge area. This time, you can activate the bridge leading to the West Area and continue searching for the vaccine.
As soon as you enter, collect the Research Lab Digital Video Cassette and a Hand Grenade from the corpse beside the wall. At the far end, beside an Item Box, you will find a circuit breaker. You already know what to do to activate it: use the Signal Modulator one final time. Once the power has been restored, you can watch the video on the television beside the Item Box.
You can read William Birkin’s Inbox on the nearby computer. In the next room, there is a Blue Herb beside the exit. Collect the High-Grade Gunpowder (White) in the following room and continue along the only available route.
Once you reach P-4, you will find a computer where you can read the Research Diary. On the northern side of the room are another container of Large Gunpowder, some High-Grade Gunpowder, a Red Herb, and a safe area. You do not need to be a genius to know what is coming, so take your best weapons from the Item Box, along with as much ammunition and as many healing items as you can carry.
Examine the tank on the other side of the room containing the Item Box and typewriter. You will automatically obtain either the vaccine or the sample, depending on which character you are playing as.
You now need to retrace your steps to the beginning of the level and return to your unconscious partner. As expected, a cutscene will begin when you are halfway back. It is time to settle a certain matter once and for all.
In this form, Birkin is much stronger, but he is also very slow. Use this to your advantage and unload entire magazines into him, especially into the giant eye, his weak point. Bear in mind that he can throw the blue containers scattered around the area, causing an explosion. If you see him pick one up, try to take cover behind one of the obstacles. If you hit one of his eyes while he is carrying a container, he will drop it on himself and blow it up in his face.
After taking enough damage, he will transform and become larger, and his eyes will reappear. The fight is largely the same, except that if he grabs you now, you will probably die instantly.
Once you have dealt enough damage again, a cluster of eyes will appear on his chest and he will move to grab a gigantic column. Move away from the center of the screen to avoid being struck by it, then fire a few more shots to finish him off.
There is ammunition scattered throughout the combat area, so use it to your advantage. Once you defeat him, remember to collect everything before continuing.
With Birkin out of action, a platform lift will activate in one of the corners, allowing you to leave the area.
Return to your partner in the northern section of the Laboratory. After the cutscene, you can use the elevator in the central bridge area to escape. Follow the only available route until you reach the final Item Box and typewriter. Arm yourself one last time.
When you go through the next door and descend on the platform lift, a ten-minute countdown will begin. Open the map: there is an exit in the northeastern corner. Run without stopping, and you will make it through before any of the enemies can reach you.
After descending the next staircase, go through the door on your right. Be ready, because the game will now follow a different path depending on your character.
The door will be locked, but your partner will open it for you while you fight off the Ivy Zombies. Once the door opens, run through it and eliminate the burning zombie to avoid any unpleasant surprises.
Keep running without stopping. When you reach the train platform, enter the train and collect the Joint Plug. Picking it up will trigger a cutscene. Afterward, leave the train and enter the adjoining room to insert the plug into the control panel.
Before leaving, collect the Minigun beside the door. You are going to need it. Approach the train to continue... and face Birkin once again.
Shoot him with everything you have. This is actually the easiest battle of them all, as you now have the Minigun and there are plenty of eyes to shoot. He will sometimes cover them, however, so make sure you aim carefully.
If he climbs onto the walls, shoot his eyes to knock him down. He is preparing to slam into the ground, which will delay the elevator even further. Once he falls to the floor and begins crawling, keep your distance and continue firing while retreating. It will not take long to finish him off.
At this point, you have completed Scenario A. You still need to complete Scenario B with either Leon or Claire, depending on which character you used for Scenario A.
The Tyrant will appear one final time. Land a couple of well-placed shots on his oversized head to knock him down, then run through the door. Another cutscene will begin as you cross the walkway, leaving you on a lower platform. Go through the door and collect the Joint Plug from the table.
Step onto the elevator platform, insert the plug into the control panel, and activate it.
First of all: you cannot kill him. You only need to survive.
The Tyrant has lost his coat, revealing his weak point: the heart in the center of his chest. The problem is that the coat acted as a limiter on his strength, and he is now much more agile. His attacks generally consist of three-hit claw combos when he gets close enough. You can avoid these simply by moving backward.
After taking some damage, if he is far away, he will crouch and leap toward you. He will ALWAYS cover enough distance to reach you, so do not run away. Instead, run straight toward him and pass by his left arm. This should be enough to avoid the attack, provided you see it coming.
As explained above, you only need to shoot him to slow him down. The elevator will continue to rise until a cutscene begins. An Anti-tank Rocket Launcher will appear in the middle of the elevator, finally allowing you to eliminate this gigantic pain in the ass.
All that remains is to continue toward the train. You can use another rocket against the group of zombies that comes through the door, and then you will complete the game.
Note: During a 2nd Run, you will still have one more boss to defeat during the game’s "alternate" ending.
