Underground Lab & Escape

Leave Sherry resting in the office (Green Herb, Acid Grenades, a storage chest, typewriter, and Ink Ribbon here) and head into the corridor with a generator at its center — it won't start without a part yet. Take the door with blue lighting into the east area. Through the double doors is a freezing room with a First Aid Spray and a Fuse Box — use it on the machine at the room's center to assemble the Main Fuse, then bring it back to the generator hallway and use it there to restore the lab's power.

Take the door with red lighting into the west area. At the end of the hall, a bedroom holds a computer with the lab's security manual file and a chair with the User Registry file — reading it reveals a username you'll need later:

Using this computer also lets you release P-Epsilon gas through the facility — it weakens some B.O.W.s like Lickers, but strengthens Ivy plants. In the locker here you'll find Bowgun ammo and a planter with Blue Herbs.

In one corner of the bedroom, burn away the tentacles blocking a vent (Incendiary Grenade or the Lighter) to reach a room with two Evolved Lickers — tougher than regular ones. Clear them for Explosive Grenades and Ink Ribbon. Back in the hallway, open the blinds to face two Ivy plants (Incendiary Grenades make quick work of them), then push on toward the stairwell — a third Ivy and two Green Herbs are here too.

Down the stairs, clear three more Evolved Lickers along the corridor (three Green Herbs nearby), then reach a control room full of monitors — examine the lit one for a Lab Map. Grab the Weapons Locker Key from the storage chest.

Use the Weapons Locker Key on the lit locker in Lab P-4 for Explosive Grenades, then clear the five zombies inside and grab the Lab Keycard from a desk.

Optional: Set Up Leon's Playthrough

Back in the east area, use the Lab Keycard to reach a room with a giant moth — kill it, destroy its larvae, then use the computer to register your GUEST login. This isn't required to finish Claire's game, but it unlocks a door for Leon's own playthrough later.

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A cutscene follows with Annette, attacked by William before she dies — she hands Claire the Vaccine Synthesis File needed to cure Sherry, and the lab's self-destruct system activates.

Use your login on the computer beside the east area's double doors — it asks for a second user you don't have access to (this is what registering earlier unlocks for Leon). Use the Lab Keycard on the central door and discard it to enter another lab: clear five zombies, flip the wall switch to power the machines, then use a Vaccine Cartridge on the synthesis machine and activate the panel across the room to produce the Base Vaccine — an MO Disc sits on a gurney nearby. Return to Lab P-4 (watch for zombies along the way) and use the Base Vaccine on its synthesis machine to get the finished Vaccine.

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Back in the control room, grab your strongest weapons and healing items from the storage chest, then use the MO Disc on the computer beside the sealed gate in the east area corridor to open it. Push through the double doors into a large chamber full of containers — a 5-minute countdown starts before the lab self-destructs. Activate the elevator switch at the far end.

William Birkin drops from the ceiling in his third mutation.

William Birkin (3rd Mutation)

Acid Grenades do the most damage here. Once he takes enough hits, he mutates a fourth and final time — much faster and far more dangerous.

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William Birkin (4th Mutation)

Keep well clear of it and dodge every bite — it hits hard enough that you should heal immediately if it connects. Keep attacking until it finally goes down.

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Once he's defeated, take the elevator down and push forward to the train.

Boarding the train triggers the game's ending cutscene: Leon, Claire, and Sherry escape Raccoon City together, and Sherry is finally cured with the vaccine.