A second attack leaves the base in ruins; however, [[Dr. Kelvin]] opens the door to the [[Reactor (Doom RPG)|Reactor]] area. The player confronts Guerard at the entrance ot the reactor, who reveals that he is Kronos and transforms into a demon. After defeating Kronos, the player destroys the power couplings to the reactor, closing a portal to hell (the player is hindered by monsters that come through the portal). After having closed the portal, it is revealed that the [[Cyberdemon]], a combination of demon flesh and human technology created by Kronos, came through the portal at the last second. The player must defeat the Cyberdemon to complete the game.