A former law professor turned special prosecutor, John Lindsay (Edward G. Robinson) volunteers his services to the government to rid a city of its criminal underworld and racketeering problem. The roots of corruption run so deep, though, that even his own office ends up on the mob's payroll, and he turns to his law students for help. With his young assistants, he turns the city, and city hall, upside down to root out the gangsters, even when the mob makes him a marked man.