Dr Sam Waters and the VCTF are in Pittsburgh, investigating a recent series of bomb blasts at several power plants. Here Sam meets the charming bomb squad expert Coop. The flirtatious pair quickly forms a romantic bond. John immediately displays a dislike for Coop (it becomes evident later that it's the ATF and not Coop that John dislikes) and there are moments of jealously.
We see Grace do some field work when the bomber chooses the "sterile brunette" to make the money drop. During this drop the bomber detonates a bomb killing a street rat and blowing up the money.
They continue their investigation; it eventually leads them to a deranged man, with an obsession for cleanliness. They track this man to his house; he is shot and killed by Bailey when he confronted the VCTF in his yard holding a detonator. His grand plan is a bomb timed to go off and poison the city's water supply. Coop and John work together to locate and de-activate the bombs.
Meanwhile when Jack sees a photograph of Sam and Coop in the newspaper he is not happy.