Welcome to A Red Letter Day, the second level of Half Life 2. A level even shorter than Point Insertion, RLD is merely the second part of the setup for the rest of the story.
You begin in a corridor with Alyx; follow her, listening to her conversation. It seems that the rebels have a working teleporter now, instead of a difficult journey on foot. Thank God no one has to travel through the canals any more!
Enter Kleiner’s secret lab and you observe him looking for “Lamarr”. Listen to their conversation and have a look around the lab, but there’s very little for you to do until Barney gets here. When he does arrive you are told that every metrocop in City 17 is out looking for you, so it’s better that they simply teleport you to Eli’s lab. Before that however, Kleiner suggests you get into your HEV suit. Follow Barney (meeting Lamarr in the process) and you are given your old suit back, with a couple of upgrades from the last time you used it, namely the sprint function. Equipped with the suit, you can now charge it at the energy terminal on the far wall (you should now have 100 health and 25 energy). Follow the others into the next room.
In here you see the teleporter that the rebels have been working on. Stand by the wall with the plugs on and watch the proceedings. When the circuit blows, simply pick up the plug on the floor and move it towards the socket it came from to put it back in and pull the switch next to the plugs when Kleiner tells you to, teleporting Alyx.
Your turn now, stand on the platform that Alyx was on moments before. Watch as the teleporter activates and watch as everything goes wrong. Don’t worry about monsters etc, you can’t be hurt. As the trip ends, you are deposited outside Kleiner’s lab, with a couple of scanners floating around.
Jump down from the ledge and run forward before making a sharp right to cut in between the bases of the pylons towards a chain link fence. Ignore the scanners. After this you find yourself on a raised platform overlooking a freight platform. Barney greets you and gives you your first weapon; the crowbar which you can use to destroy wooden planks blocking any doorways. With this you can deal with any scanners that follow you around but the CPs are all out of reach. Don’t chase after them, just ignore them and stay in cover. Drop down to ground level and run left, climbing into a red carriage with an open door filled with boxes and crates. Run through the carriage and out the other side, but get off the tracks as a train comes hurtling past. Follow behind this train, back down the tracks towards the CPs. At the first opportunity turn left again into the third lane and up into a second carriage, this one a pale green colour with boxes and furniture. This one has a ladder leading to the roof. Climb it and jump from the roof to the next carriage and then over the fence to the other side. Continue through the door to the next level.