David Simon's masterful social commentary went back to school, quite literally, in the fourth season, which focuses on Baltimore's crumbling education system. A relevant link to its first three seasons is supplied by Roland "Prez" Pryzbylewski (Jim True-Frost), who left the police department to become a teacher at Edward Tilghman Middle School, a hardscrabble institution on life support that services a low-income, drug-infested neighborhood. (Incidentally, Prez's career path is similar to one of the series' producers, Ed Burns). His eighth-grade math class includes a close-knit quartet of friends -- Randy Wagstaff (Maestro Harrell), Michael Lee (Tristan Wilds), Duquan "Dukie" Weems (Jermaine Crawford) and Namond Brice (Julito McCullum). The wisecracking Brice is ignominiously selected to be part of a university experiment studying at-risk kids, which counts a former police commander, Bunny Colvin (Robert Wisdom), as a consultant. Out on the corners, Marlo Stanfield (Jamie Hector) strengthens his grip on the city's West Side narcotics trade once dominated by the Barksdale gang, and with his cold-blooded lieutenants, Chris (Gbenga Akinnagbe) and Snoop (Felicia Pearson), devises an ingenious method to hide the collateral damage of his ascent from the law. This sleight-of-hand bedevils detectives Freamon (Clarke Peters), Greggs (Sonja Sohn) and Bunk (Wendell Pierce). The trio are flummoxed by the lack of victims that would surely coincide with Marlo's ever-widening domain, a savage power grab that also threatens the relative peace of the New Day Co-Op under East Side pooh-bah Proposition Joe (Robert F. Chew). Meanwhile, the Democratic primary in the city's mayoral campaign pits the entrenched African-American incumbent, Clarence Royce (Glynn Turman), against Councilman Tommy Carcetti (Aidan Gillen), a scrappy politico with a savvy campaign manager in Norman Wilson (Reg E. Cathey), but a long shot to become Charm City's first white chief executive in years.