Sometimes a classroom needs more than a regular substitute sometimes you need a soldier.
Jonathan Shale (Berenger) is a mercenary and a Vietnam veteran who returns home to Miami after a botched covert operation in Cuba in which three men from his platoon were killed. He surprises his girlfriend, Jane Hetzko (Diane Venora) at her apartment and is warmly welcomed. On the outside, Hetzko is a schoolteacher at inner-city Columbus High School, an institution with a considerable gang problem. She is particularly disliked by Juan Lacas (Anthony), leader of the KOD ("Kings of Destruction") gang. While jogging one morning, Hetzko is attacked and has her leg broken. Hetzko and Shale believe this to be related to the KOD, which prompts the latter to go undercover as an Ivy League-educated, government-affiliated substitute teacher for his girlfriend's class.
Randall Thomasson is gunned down while attempting to talk his way out of a carjacking. His brother, Karl, attends his funeral and attempts to make amends with his niece, who is angry that Karl never contacted her or her father.
Students at a local college have become unusually antagonistic, and when a teacher is attacked by a gang of steroid-pumped students, Karl Thomasson—having earned a teacher's degree to facilitate his actions in the previous film—returns to the classroom to uncover the truth.
Karl Thomasson, an ex-Special Forces soldier and retired mercenary, is approached by his old army buddy Teague who gives him a mission: working undercover at a military school where Ted, Teague's nephew, is one of the cadets. Teague believes that the cadets and the student faculty are part of a white supremacist cult being run at the school. Karl accepts the mission and begins working as a history teacher at the school, seeking to expose and eradicate the cult.