

Virgil plans to hide for a while in the overgrown tracks GLaDOS made, to confuse its scanners. The assailant- which is revealed as the Aperture Employee Guardian and Intrusion System, or AEGIS- takes over many of these testing tracks in more attempts to kill the pair.

They manage to escape and enter the newer facility above the salt mines, while Virgil attempts to guide Mel through increasingly dangerous testing tracks. With Virgil rescued, he and Mel have to face the sudden flooding of Old Aperture by an unknown, all-powerful assailant. With his help, Mel ascends through Old Aperture and rescues Virgil, who has fallen off his rail. However, as it becomes more obvious that it was not an earthquake that destroyed the facility, the voice gives up and reveals himself as Virgil, a maintenance core. Guided by “Cave Johnson”, Mel picks up an early version of a Portal Gun, and then follows his instructions to “keep testing another shaft”. She is woken up an unknown amount of years later by a voice positing itself as Cave Johnson, in a ruined facility. She follows his instructions to an Aperture Short-Term Relaxation Vault, where she is supposed to sleep for only a few minutes. At the beginning of the game, Mel arrives at Aperture Science’s constructed city, guided along her way by recordings of Cave Johnson.
