Hawaii Five-O Season 1 Episode 21 (04/18/11)
Reggie Cole, an undercover police officer working for the FBI, visited his family in Hawaii. During his visit the FBI safe house was infiltrated and his wife was shot and killed. The Five-O were called in to investigate, and McGarrett continued the investigation even after the FBI said they would handle the matter themselves. The prime suspect was Jimmy Cannon, the crime boss Reggie was investigating.
Though he was wounded during the initial shoot out, Reggie escaped the hospital to seek revenge for his wife's death. The Five-O continued their investigation and found a leak in the FBI detail protecting Reggie and his family. Eventually, the Five-o caught up to Reggie before he could go after Jimmy Cannon. After further investigation Reggie and the Five-O discovered that the hit was ordered by Cannon's son, who was trying to usurp his father's crime empire.
McGarrett received another piece of evidence back from his father's tool box.