Sewers & Abandoned Factory

Head down the tunnel (two Blue Herbs along the way) into a room with a storage chest, typewriter, and Ink Ribbon — the lockers by the elevator hold a First Aid Spray, a small red table has Handgun ammo, and a desk has the Sewer Chief's Fax. Push the lockers in the middle of the room to reveal a hidden ladder behind a hatch; down it is a dim storeroom — light the lamp on the right with the Lighter for Magnum ammo, then another further in for Shotgun ammo.

Bring the Valve Handle with you and take the elevator down. A mysterious woman flees and shoots Ada — Leon saves her, but she's knocked unconscious. You now control Ada; chase the woman through the vent (dodging giant cockroaches) until she stops and identifies herself as Annette Birkin. A struggle over Ada's pendant sends Annette falling off the platform, and Ada discovers a G-Virus sample hidden inside the pendant. Cross the hydraulic bridge and head down the stairs, where Ada stays behind to recover.

Back as Leon, follow the path Ada took — a Sewer Map is on the wall. In the tunnels, go left to the end and check the corpses in the side passage for the Wolf Medal and a Small Key.

Push through two giant-spider tunnels and reach the waterfall-blocked door — the Wolf Medal alone isn't enough, so head left through the double doors to the hydraulic bridge room instead (Blue Herbs in a planter here for spider poison). Use the Valve Handle on the wall socket to lower the bridge, cross, and use it again on the other side to raise it back up (two Green Herbs, a typewriter, Ink Ribbon, and Shotgun ammo are here too). Continue to the garbage dump, where Ada is waiting — approach for a cutscene where she bandages Leon's wound, then she starts following you again.

Climb the stairs, cross the hydraulic bridge, and go left to grab the Eagle Medal off a corpse and the Sewer Chief's Diary. On the right side of the bridge, use the Valve Handle to stop a turbine, then climb up and through the ventilation tunnel and back down. Push through the corridor to the waterfall door and use the Wolf Medal and Eagle Medal on its panel to stop the water. Cross into the tunnel beyond, reach the cable car platform, and activate the controls to board.

A creature claws at the cable car's roof during the ride — dodge its swings until it gives up. On arrival, use the Lighter on the flare cannon to spot the Weapons Locker Key in a corner. Push through a hallway with four zombies and check the corpse at the end for the Shotgun Part — combine it with the Shotgun for more firepower, a 7-round capacity, and heavier recoil. Continue through the next hallway (four more zombies, a Green Herb, and a Blue Herb) and climb to the control room — Ada stays behind to operate its panel. Grab Magnum ammo and Shotgun ammo from the console and a First Aid Spray from the shelf.

Out on the empty platform, grab Handgun ammo by the barrels and the Factory Map on the wall. Take the small elevator down, then follow the hallway to its end for a key on the control console. The security camera shows the Tyrant closing in — it's best knocked down here since the corridor is narrow (Shotgun ammo). Return to the control cabin and use the key on the panel next to Ada to bring the giant elevator back to the platform.

Head to the elevator and activate its panel — Leon and Ada step inside as it descends into the depths. A creature slashes into the cabin, wounding and knocking out Ada. Search the toilet inside for Magnum ammo, then step out to investigate.

It's William Birkin, mutating further.

William Birkin (2nd Mutation)

Keep your distance and hit him with the Magnum or Shotgun. If you retreat too far he'll leap right next to you — dodge every time he jumps.

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Once he's down, return to the elevator — it stops mid-descent, and Leon leaves Ada in the cabin to recover. Exit through a vent outside the elevator; it leads to Umbrella's underground laboratory, and the elevator resumes its descent on its own.