While on break Malloy and Reed learn that an old "friend" Jennings Thornton is back. He likes to play cop - a cop Buff. First call is to a store where a young inexperienced clerk had an expensive ring swapped for a cheap one. This is followed by their "friend" Thorton calling in a drunk driver he encountered. A call about a robbery at a store results in a shootout in the parking lot but the shooter has a flak jacket. Thorton runs down the shooter with his car to end it but putting Reed in danger . The officers take a call at a parking lot where a minor accident has occurred. The woman has no ID and appears to be the woman who stole the ring. They arrest her but the clerk cannot identify her. They receive another call where Thorton used a gun to arrest two young men for stealing mag wheels. However, they were the legal owners of the wheels and the roles are reversed with Thorton under arrest. Mac arrives to say they found the ring on the woman at Central Booking making for a very good day.