Trevor Garfield is an African American high school science teacher at Roosevelt Whitney High School, a high school in the Bedford-Stuyvesant neighborhood of Brooklyn. Dennis Broadway, a gangster student to whom he had given a failing grade threatens to murder him, writing the number 187 (the California police code for homicide) on every page in a textbook. The administration ignores the threat, and Dennis ambushes Garfield in the hallway, stabbing him in the back and side abdominal area multiple times with a shiv.
Fifteen months after surviving, Garfield, now a substitute teacher, has relocated to John Quincy Adams High School in the San Fernando Valley area of Los Angeles, but trouble starts again when he substitutes an unruly class of rejects, including a Chicano tag crew by the name of "Kappin' Off Suckers" (K.O.S.). Their leader, Benito "Benny" Chacón, a felon attending high school as a condition of probation, makes it clear to Garfield that there will be no mutual respect.