The Combine's first appearance is in "Half-Life 2". Through the early stages of the game, Combine Civil Protection units pursue Gordon Freeman through City 17 after he accidentally reveals his presence to Wallace Breen. Due to Freeman's actions in "Half-Life", Breen sees Freeman as a major threat. As Freeman escapes the city, Civil Protection units raid the resistance base of Black Mesa East and capture resistance leader Eli Vance, who is transferred to holding facilities at Nova Prospekt. Freeman and Vance's daughter Alyx break into the facility to rescue him, but Eli Vance is teleported to the Combine Citadel by double agent Judith Mossman. However, the strike against Nova Prospekt is seen as the start of a revolution by the citizens of Earth, who take up arms against the Combine. In response, Combine Overwatch are deployed to City 17, and heavy street fighting takes place. Freeman manages to infiltrate the Citadel but is captured and taken to Breen. Mossman allows Freeman to break free of his captivity, and Breen flees to the Citadel's trans-dimensional teleporter, intent on escape. However, Freeman destroys the teleporter's reactor before Breen can escape, causing a large explosion that destroys the top of the Citadel.