The action takes place in a science fiction environment. In the single-player game, the player is a human soldier (known only by his alias, 'Bitterman') taking part in 'Operation Alien Overlord', a desperate attempt to protect Earth from alien invasion by launching a counter-attack on the home planet of the hostile cybernetic Strogg civilization. Most of the other soldiers are captured or killed almost as soon as they enter the planet's atmosphere, so it falls upon the player to penetrate the Strogg capital city alone and ultimately to assassinate the Strogg leader, the Makron. Unlike Quake, where hardware accelerated graphics controllers were supported only with later patches, Quake II came with OpenGL support out of the box. The latest version is 3.21. This update includes numerous bug fixes and new maps designed for multiple players deathmatch. Version 3.21, available on id Software's FTP server, has no improved functionality over version 3.20, it simply is a slight modification to make compiling for Linux easier. Quake II uses an improved client server network model introduced in Quake.