Get back to the main area and climb on the platform on the left (active point is left from the ostrich standing on the track). Go up the stairs that can be seen in the passage on this side of the track. You will see Oscar there. During the conversation, the automaton will voluntarily offer to go out and open the conduits so that the bats can leave.
As Oscar (achievement: I is somebody else), go towards the bottom of the screen, take the stairs, and go straight ahead - towards the exit from the metro station (however, if you go back and enter the airlock on the left, the one from which Oscar entered, and then press the red button near the glass, behind which there is Kate, a few times you get Ironic, ain't it? achievement).
Outside, go straight ahead (towards the bottom of the screen) and to the right. From the monument, behind which Oscar hides, go a few steps inwards and then run towards the fire truck - pass the truck on the right. Right behind the green van, go to the near sidewalk.
Go past the building with the partially boarded windows and enter the next one through the open door. It's a small bank.
Proceed towards the passage on the right - you will get to a room with barred windows and an open safe (on the left). Take the shears that are lying on the floor next to it.
Leave the bank, walk off the sidewalk onto the street and proceed right, to the fire truck. Enter it from the driver's side.
Open the glovebox in front of the passenger's seat. Zoom in and shuffle the things inside in order to extract the ignition key, that is among them somewhere. Insert it into the ignition (on the right side of the steering wheel). When the truck finally starts, Oscar should pull down the lever that's on the right side of the steering wheel. Ocar will be able to get drive near the metro staton.
Setting up the ladder
When the automaton exits the truck, go to the back of the truck and climb the two small ladders in order to get to the ladder control panel.
Zoom in. Turn the upper wheel to the right with your mouse, so the ladder is perpendicular to the metro station building. Then turn the lower one right to raise the ladder so that it's on roughly the same height as the air conduits on the roof. Then pull the lever to extend the ladder.
Take the ladder (active point on the bottom-right). Zoom in, use the shears on the conduits' grating (active point to the far left). Having done what you needed, get off the ladder (active point behind Oscar).