 A series of bomb blasts at power plants draw Sam, Bailey and the rest of the task force to Pittsburgh, where Sam meets a charming ATF bomb squad dismantler, named Nick Cooper, and the flirtatious pair quickly form a romantic bond. Even so, their primary focus remains on targeting a deranged man, with an obsessive fetish for cleanliness, who targets Grace as his liaison between the authorities, while he is working on a masterwork blast to poison the city s water supply in just hours.