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From HalfLife 2 Knowledge Base

This chapter begins after you're rescued by Alyx from a group of Combine soldiers. She leads you through a small maze of corridors and into Dr. Kleiner's lab.

Once inside, there's plenty to look at, as well as listen to. Dr. Kleiner, Alyx, and Barney all have a lot to say here. Shortly you're given your HEV suit, and since you're not terribly far away from your first fight, you'll want to charge it up on the other side of the lab.

Dr. Kleiner in his speech says that the teleportation machine is ready to be tested, and to commemorate its first use, they were going to have a double transfer. You follow Alyx, Barney, and Dr. Kleiner into a room off of the main lab and help as Alyx is teleported to her father. Next, it is your turn to be teleported. When you try it, however, Dr. Kleiner's pet headcrab, Lamarr, jumps into the portal and makes it malfunction, and you end up right where you started, but not before you are briefly sent to what appears to be Dr. Breen's office at the Citadel, Dr. Vance's lab, some beach location, underwater, and finally behind Dr. Kleiner's platform in the lab.

Barney will give you your trusty crowbar soon after the teleportation mishap, and you'll need it to break through some planks blocking your way. Here you wind up in a train yard, being shot at by Combine soldiers. There's not much you can do here except run and find the exit as quickly as possible.