Arriving at White Forest, Alyx and Gordon reunite with Dr. Kleiner and Eli Vance, and Alyx finally delivers the transmission packet acquired in Episode One to them. They also meet Dr. Magnusson in person, another former Black Mesa scientist who is egotistical, verbose, authoritarian, and holds a grudge against Gordon. Gordon and Alyx learn that the White Forest team is preparing a special rocket which they plan to use, in conjunction with Alyx's data packet and the satellite array launched during the events of Half-Life, to close the Combine superportal. They are interrupted when a Combine attack penetrates the base. Gordon defeats the attack force, consisting of Hunters and soldiers, and closes the silo doors that are allowing access to the facility.
After successfully repelling the attack, Gordon meets up with Alyx, and the two return to Dr. Kleiner and Eli who have completed decoding Dr. Mossman's message. It reveals that the "project" is none other than the Borealis, an Aperture Science vessel which mysteriously disappeared some time before and is rumored to carry powerful technology. Dr. Kleiner suggests using the technology of the Borealis against the Combine, while Eli insists that it be destroyed to avoid another Black Mesa Incident. Initially, Eli wants to follow Dr. Mossman to rescue her; however, he becomes convinced that his own knowledge of the Resistance is far too sensitive for him to risk capture by the Combine, and Alyx promises that she and Gordon will go after Dr. Mossman. After a call from an irritated Dr. Magnusson, Dr. Kleiner leaves to assist him in the final preparation for the launch of the rocket. As the G-Man appears on the screen behind her, Alyx delivers his message to Eli: "Prepare for unforeseen consequences." Upon hearing this, a shocked Eli nearly collapses and, in private, informs Gordon that the G-Man spoke those same words to him just before the Black Mesa Incident. Eli expresses regret for not aborting the test that led to the Incident and over the G-Man's present influence over Alyx.
They are soon interrupted, however, as they are informed a larger force of Combine advancing on the base, complete with Striders and Hunters. Dr. Magnusson introduces Gordon to the Magnusson Device, a sticky bomb designed to destroy Striders, and informs Gordon that keeping the Striders away from the silo is crucial, as a single Strider could destroy the rocket. Using the Gravity Gun to launch the devices, Gordon manages to defeat the attack force in the valley around the base.
This chapter contains examples of:
- Hold the Line: The second major instance of the game: much of the combat in the chapter involves Gordon defending the valley from a constant string of Striders and the Hunters supporting them, keeping the former away from the silo to protect the rocket.
- Once Killed a Man with a Noodle Implement: A Rebel-in-Training at the White Forest Base first claims to have used AR3s (which don't exist), then claims to have killed Hunters (alien tripod cyborgs that are rather deadly) "with his own hands". The one giving advice to the others immediately calls him on his BS and refuses to continue the lesson until that one leaves.
- Privacy by Distraction: Eli sending Alyx to make tea so he can tell Gordon about the G-Man.
- Request for Privacy: Eli Vance asks his daughter Alyx to get him some tea, so he can reveal to Gordon his acquaintance with the G-Man and his role in the Black Mesa Incident, as well as ask him to destroy Borealis without trying to use it—something he obviously doesn't want Alyx to know beforehand.
- Suspicious Videogame Generosity: The valley's buildings are not only equipped with respawn points for Magnusson devices, the shelves also restock with batteries and medkits to keep you alive as you fight the numbers of Hunters and Striders outside.
- Trial-and-Error Gameplay: The White Forest defense is already bad itself, but Episode Two has an achievement for getting through the entire segment without losing a single building. This can be problematic because sometimes Striders will spawn as sprinting variants that charge their target building and then immediately destroy it, and the game will create situations where it'll spawn a slow Strider to get the player's attention before deploying a fast one to wipe out a building before the player can even get close to it, if they engaged the slow Strider already. And this exact setup happens with the very first two Striders that attack the base. Better make it a habit to manually save religiously, or look up a guide on what Striders will spawn from where.
- Trigger Phrase: Not exactly a phrase, but the silhouette of the G-Man appearing on a monitor causes Alyx to go into a trance and deliver a message to her father. She has no memory of this. Makes one wonder how much control the G-Man has over her.
