Detective Steve McGarrett (Alex O'Loughlin) was once a naval officer who received the Medal of Honor. After retiring, he became a police officer. In order to investigate his father's murder, he returned to his hometown of Oahu (the main island of the Hawaiian Islands). The governor of Hawaii believed that Steve was a rare talent and insisted on keeping him on the island to work. She wanted Steve to form an elite team dedicated to investigating serious cases - he set the rules and she provided support behind the scenes. This team named "Five-0" (50) does not go through the motions or play tricks. As long as they can catch the biggest gang leader on the island, they will not mind even if the sky collapses. Steve readily agreed to the governor's request and began to "recruit troops". The first to join the "50" serious crime team is Detective Danny Williams (Scott Caan), who is called "Danno" by everyone. He used to work in the New Jersey Police Department and was recently transferred to the Hawaii Police Department. He likes the urban life with tall buildings and has little interest in sunshine, beaches and endless coastlines. However, in order to give his 8-year-old daughter a healthy growth environment, he vowed to protect the safety of the island. Then joined by Chin Ho Kelly (played by Daniel Dae Kim). He used to be a detective in the Honolulu (capital of Hawaii) Police Department. Because of a false corruption accusation, he was demoted to the Federal Security Patrol as a patrolman. He was once a disciple of McGarrett's father. Chin's cousin Kono (played by Grace Park) was born and raised in Hawaii. She is strong and competitive, and her personality is a bit like a tomboy. She just graduated from the police academy and is eager to prove her ability in her job, so she took the initiative to ask to join the "50" Major Crimes Unit. With the help of the "50" Major Crimes Unit, McGarrett vowed to solve the case of his father's murder and let his father rest in peace. At the same time, he will lead his comrades to clear all the evil on this beautiful island, so that Hawaii, the "50th" state of the United States, will always be a paradise on earth.