The authorities looking into a case are lead to believe that a former gang member was behind a police officer's death, a death they think was a revenge killing for the death of the former gang-member's brother. However, when Charlie gets a hold of and analyzes the data, his findings lead the FBI through a tangled web of suspects and dirty cops. Meanwhile, Don and Liz's relationship moves to the next level.
In other developments, Alan Eppes is sued for a driving range project he designed that has become a neighborhood nuisance. Dr. Mildred Finch asssts him in finding out what went wrong and who is responsible.