Quake 4 gameplay of the last level and end boss battle.
The Quake 4 single player mode continues the story of Quake II by pitting the player against a cyborg alien race known as the Strogg. The game follows the story of a marine named Matthew Kane who is a member of the fabled Rhino Squad.against the Strogg.
After performing a number of tasks, such as destroying and capturing Strogg aircraft hangars and defense systems, Kane and his remaining squad members make it to the USS Hannibal. There they are given their next mission: infiltrating one of the Strogg's central communication hubs, the Tetranode, with an electromagnetic pulse bomb in the hope that it will put the main Strogg Nexus in disarray. Kane is tasked with defending the mission convoy, which takes heavy casualties. After many setbacks, including the destruction of the EMP device by a Strogg ambush, Kane is left to complete the mission, assisted only by Private Johann Strauss and Lance Corporal Nikolai "Sledge" Slidjonovitch. Strauss figures out a way to destroy the core by shutting down its coolant systems. As Kane reaches the entrance to the Tetranode, however, he is greeted by two rocket-equipped network guardians - as well as the newly constructed Makron. The Makron easily defeats Kane and knocks him unconscious.
When Kane finally awakens, he finds himself strapped to a conveyor belt in the Strogg "Medical Facilities", a structure used for turning those captured and killed by the aliens either into protein food or additional Strogg units. In a long and gruesome first-person cutscene, Kane is taken through this stroggification process which violently replaces much of his anatomy with bio-mechanical parts. Before the final controlling neurochip implanted in his brain can be activated, though, Rhino Squad bursts into the facility and rescues Kane.
The commanders realize that Kane's Strogg physiology has opened up new possibilities for defeating the Strogg, as he can be used to infiltrate locations previously impenetrable to human forces.