A tunnel full of infected, a flooded stretch beyond it, and the game's last workbench.
The tunnel holds Bloaters, Clickers and Runners in the open, so sneak it instead of fighting. Keep a whole shiv for the door past the workbench: wait for a Clicker to walk off rather than spend the shiv on it. The workbench here is the last in the game, so bring your parts. A missed pickup can be collected after the credits with Chapter Select.
Firefly Pendant: Natalie HooHidden spoiler – activate to revealCollectibleMinor spoiler
Location
Bus Depot · Underground Tunnel – Past the broken-down bus, the road turns left toward a ramp with a yellow city bus parked across it. Walk around the bus. The pendant is on the ground between it and the wall, by the bushes. If you've reached the tunnel, you've gone too far.
Bus Depot · Underground Tunnel – Crouch and keep to the right wall until you pass the lorry stood on its end, then take the doorway on the right. They're on the floor in the right corner.
Bus Depot · Underground Tunnel – Go on through the side rooms and up the stairs, strangling the three Runners from behind. They're on a shelf in the room at the far end.
Training Manual: Bomb ShrapnelHidden spoiler – activate to revealUpgradeMinor spoiler
Location
Bus Depot · Underground Tunnel – Crouch and keep to the right wall past the first Bloater, waiting for each Clicker to walk off. Take the doorway on the right just past the upended lorry, then go through the side rooms and up the stairs, strangling the three Runners from behind (you're past this if you took the shelf parts). You come out facing a white box truck, a horse head in red on its side: climb on to it, and the manual is on top.
Past the Bloaters, boost Ellie, swimHidden spoiler – activate to revealQuest stepMinor spoiler
Location
Bus Depot · Underground Tunnel – Let the right-hand Clicker wander off, then slip past behind the Bloater and keep right (the left wall works too). Boost Ellie on to the trailer at the end: the crate she drops makes noise, so climb up at once and drop down the far side. Dive under the truck ahead, climb the fire truck and bring its ladder over to Ellie.
Comic: CatalysisHidden spoiler – activate to revealCollectibleMinor spoiler
Location
Bus Depot · Underground Tunnel – From the top of the truck, step on to the vent ducts along the left wall and follow them to the end, just short of the broken part. The comic is there. Turn it over when you read it.
Boost Ellie over the fenceHidden spoiler – activate to revealQuest stepMinor spoiler
Location
Bus Depot · Underground Tunnel – Drop into the water and join Ellie on the right at the locked gate. Boost her over the fence where there's a gap, on the left. A Clicker goes for her, so kill it through the gate, and she opens it for you.
Bus Depot · Underground Tunnel – Go through the gate. It stands along the far right wall of the room, by the next door. Open it even with nothing to spend, and finish the Revolver here if Combat Ready is still open: no bench comes after this one.
Bus Depot · Underground Tunnel – Go through the door by the bench and up the few steps. Where the corridor forks, turn right instead of left. The door takes one whole shiv: a part-used one won't open it. Take everything inside.
Bus Depot · Underground Tunnel – Go back to the fork and follow Ellie to the flooded room, then dive in and swim out by the right-hand doorway. In the dark room, climb the shelf and the pipes, walk round and push the plank down, then float Ellie across on it. The ladder she lowers breaks: prop the piece against the wall behind you, climb up, pull it after you and lay it across the gap. Walk on along the flooded stretch, keep up with the prompts when they come, then swim to Ellie. A scene ends the chapter.