In Season 4 of Blue Bloods, tensions arise as Frank and Erin disagree over a case that involves the death of a cop. Later, Danny is forced into the role of lead hostage negotiator as Erin's life hangs in the balance. Meanwhile, Jamie's conduct is called into question--more than once. Follow the Reagans, a multi-generational family of cops as they continue to dedicate their lives to New York City Law Enforcement.