All 21 episodes from the fourth season of the American crime drama created by Dick Wolf and Craig Turk. Centred around the office of the Federal Bureau of Investigation, the series follows a team of special agents who bring together their skills and expertise in order to solve major crimes on the streets of New York. In this season, the team investigate groups of extremists, hunt for serial killers and track down a deadly chemical weapon. The episodes are: 'All That Glitters', 'Hacktivist', 'Trauma', 'Know Thyself', 'Charlotte's Web', 'Allegiance', 'Gone Baby Gone', 'Fire and Rain', 'Unfinished Business', 'Fostered', 'Grief', 'Under Pressure', 'Pride and Prejudice', 'Ambition', 'Scar Tissue', 'Protective Details', 'One Night Stand', 'Fear Nothing', 'Face Off', 'Ghost from the Past' and 'Kayla'.