he second season of the CBS crime drama series Hawaii Five-0 premiered on September 19, 2011. The season continues to center on the "Five-0", a specialized task force established by the Hawaiian Governor that investigates a wide series of crimes on the islands, including murder, terrorism and human trafficking. The second season introduces a new governor, Sam Denning, after the murder of his predecessor, Patricia Jameson. However, unlike Jameson, Denning orders new changes to the task force. The season includes two more main cast members, Masi Oka, who recurred in the first season, and Lauren German, who departed after episode 16. Alex O'Loughlin appears briefly in episode 20 and does not appear in episode 21 as he was seeking drug treatment for pain management medication during the production of those two episodes.

Overview from themoviedb.org