Infection is the fourth level in the campaign. It takes place at an island that Strike Force Squad have parachuted down to after their cargo plane had been destroyed in the previous mission. As the player arrives, however, some of the teammates are firing at him. This is due to them being infected by the toxin, but it is unbeknownst to the player however. He asks his only teammate not firing at him, Jenkins, about the teammates. Unfortunately, he has no idea. To make matters worse, Jenkins starts to develop the urge to shoot the player. This leaves him no choice but to finish off his teammates.
Transcript[]
Mission[]
The Soldier parachutes down to the ground, where he sees his teammates, except for Jenkins, mysteriously attacking each other.
Jenkins: Sir, thank god you're here! Something's wrong with these soldiers...
Soldier (Player): What do you me-- Whoa, hey, watch your fire!
After 6 kills for the Uninfected...
Jenkins: Sir, I don't feel so... auugh!
Soldier: Jenkins! Friendly Fire!
Jenkins: YAAGHH--AARRAAAUGH!
Jenkins turns into one of the infected.
Soldier: What the hell is this place...
After 15 kills for the Uninfected, the mission is accomplished.