Together, we go to Missile Bay 1, where Dr. Kleiner and Magnusson are making the final preparations to launch a satellite into Earth orbit. We see the tame headcrab, Lamarr, climb into the satellite.
If we carried the dwarf this far from the start of the game, we now place him inside the satellite and close the hatch behind him.
Eli, Alyx, and Kleiner leave to decipher the received data. Magnusson sends us down to find out the cause of the alarm in Missile Bay 2.
We descend into the open hatch via the stairs, then the elevator. On the way down, we turn the valve to shut off the steam. We approach the locked door, try lowering the lever on the right, pressing the buttons on the left, and then simply stand in front of the small glass panel to the right of the door. A Vortigaunt in a scientist's coat will spot us through the glass and open the doors for us. (In the office on the left, behind a large cistern, we see a small room—a reference to the TV series "Lost").
We quickly move along the entire length of the room and emerge from under the floor near the far wall. We kill two Hunters, then another Hunter will appear along with a pair of flying Manhack blades. After defeating them, we go to a side room with an open roof. In it, we climb up the suspended catwalk, reach a pipe, shut off the steam with a valve, and climb onto the balcony.
We follow the red corridors, here we exchange fire with soldiers and portable turrets. We pass through the flooded room and climb up the inclined corridor.
On the top floor, in the control room, there's a machine gun, with several Combine behind it. We don't attack directly; instead, we move down the right corridor, blasting through crates and crawling between shelves. Standing to the side, we toss a grenade at the enemies and finish off the survivors. We climb inside through the glass above the machine gun and press the lever. The upper doors will slowly begin to close. Above us, in the air, we see an Advisor and several more soldiers descending on ropes. We man the machine gun and shoot anyone who tries to get down to us. After the shaft closes, all the side doors open. Alyx and a Vortigaunt will arrive. We finish off the remaining soldiers.
Kleiner leaves to decipher the superportal's closing code, and we stay behind to discuss our future plans. An image of the G-Man flashes on the screen, and immediately afterward, Alyx delivers a message to her father: "Be prepared for unforeseen consequences." Eli will become ill, and he will tell her that in Black Mesa, the G-Man gave him a teleportation crystal with the same words, which is what started all the trouble.
A large-scale Strider attack is being prepared for the base, and we need to help the resistance from the outside. Follow Magnusson into the next room. (Here, behind the net, under a pile of crates, is the cover of a Black Mesa HEV panel.)
We go out to the garage and grab the bazooka, if we didn't find it earlier. We get into the upgraded car. The radar now shows both enemies and buildings around us, and there's a special place in the back for transporting one mine.
We look at the valley map. Striders will attack from the three upper ravines. We need to defend the buildings, each of which contains first aid kits, ammo, and a mini-teleporter for obtaining mines. We're heading to the sawmill, where a squad is waiting for us.
At the sawmill, listen to the briefing. The Striders will be accompanied by small hunters; they can destroy the bombs with their shots, so they need to be eliminated first. We can run over the hunters with a car. The Strider itself is destroyed by the explosion of a single sticky bomb.
The area is vast, with Striders attacking from all sides, so to navigate, we monitor the car's radar and listen to the dispatcher's instructions; he'll tell us where the next Strider has been spotted:
cranes on the left, a sawmill in the center, and a water tower on the right.
A total of 13 Striders will attack us, divided into three phases.
- 1 strider, cranes, we are waiting for him at the sawmill.
- Strider 2, sawmill, wait to the right of the sawmill. This strider is trying to destroy the building, so it's faster than the others. Destroy the first strider near the sawmill to avoid a long return, immediately grab the second mine, and drive towards the second strider. If the enemy manages to fire a blue beam, the sawmill will be destroyed.
- 3rd strider, at the water tower, wait at the right building.
- 4th strider, at the cranes, waiting at the left building.
- 5 strider, sawmill, we are waiting in the center.
- 6th strider, near the water tower, we'll leave it for later.
- Strider 7, near the cranes. Once we kill Strider 5, Strider 7 will appear. We immediately drive towards it, ignoring Strider 6. Strider 7 runs quickly and tries to blow up the building on the left. We drive to this building, take out a mine, and wait for the enemy to approach. When he starts aiming, throw the bomb and detonate it. If we don't get there in time, he'll destroy the supply shed on the left.
- Strider 8, near the sawmill. Strider 6 is walking near the right barn, and Strider 8 will quickly run in the same direction. We drive to the right building, kill the Strider 6 that missed us, and then throw a mine at Strider 8. If we don't get there in time, he'll blow up the supply barn on the right.
- 9 Strider, sawmill. 10 Strider, cranes. 11 Strider, tower.
- 12 Strider, sawmill. 13 Strider, cranes.
Of the 13 striders, only 3 can destroy structures; the rest simply pass by. Destroyer striders are highlighted in red (Strider 2, 7, 8); we destroy them first. Proceed to the final chapter.