In the season premiere episode, McGarrett and Wo Fat make a narrow escape from maximum security, gunman storm Five-0 headquarters and Catherine is taken hostage. Now, in McGarrett's quest to save Catherine, he must break the rules and go head-to-head with new SWAT Commander Captain Grover (Chi McBride). Meanwhile, Kono and Adam's secret location in Hong Kong is compromised.
A Texas Ranger comes to the island to find his missing daughter, and the Five-0 team gets involved when hug happens. Meanwhile, Kono and Adam's hidden location.
A double hug forces the Five-0 team to bring in a conspiracy therapist to help them find a missing artifact tied to the killings.
Five-0 investigates the hug of a wedding crasher, and their prime suspect is the runaway bride. Meanwhile, Danny makes a big decision regarding his relationship with Gabby.
As Catherine's seemingly harmless surveillance job takes a deadly turn, Adam considers making the ultimate sacrifice to save Kono.
When Halloween comes to Hawaii and a zombie-like man is shot, Five-0 races to stop a madman who is conducting experiments on humans.
While working the hug case of an undercover ATF agent, McGarrett and the Five-0 team are tasked with watching Mary's newly adopted baby after she gets sick.
McGarrett and Grover must work together to protect national security after they are tasked by the governor to serve a warrant to a young computer hacker. Nick Jonas guest stars as the young computer hacker.
As Thanksgiving approaches, Five -0 investigates the hug of a secret service agent just as the president travels to O'ahu. Also McGarrett's Aunt Deb visits, bringing with her a shocking secret.
The attempted hug of a Pearl Harbor veteran leads Five-0 to use decades old evidence to investigate a deadly crime committed within the internment camps on Oahu during World War II.
Chin's life is put in danger when a hug investigation reveals that the person behind the crime may be a serial hugger. Meanwhile, Danny and Grace find a mysterious puzzle box washed up on the shores of Oahu.
Captain Grover is aided by McGarrett in his search for a friend who has disappeared, after it seems like he's committed hug. Kono persists in her quest to find Adam.
Internal Affairs questions Chin about his father's hug 15 years earlier and how his then-new relationship with Malia and her family might have hurt the investigation.
McGarrett and Danny are kidnapped by an escaped convict who wants Five-0 to prove he is innocent. Meanwhile, Grace gets into trouble when she punches someone at school.
While Five-0 investigates the hug of a real estate agent whose body was found in the walls of one of his listings, Danny is thrown when his mother comes to Oahu with shocking news.
Five-0 investigates a triple hugging connected to a downed top-secret Chinese satellite, while Grover takes Danny's mother on a ride-along. Melanie Griffith and Jorge Garcia return.
Five-0 aims to uncovers the sordid truth when a girl is taken from her home and her father is shot in the process. Meanwhile, Danny tries to get his parents back together and Jerry deciphers a code he found on the bottom of McGarrett's champ box. Melanie Griffith and Jorge Garcia return and Tom Berenger guest stars.
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Five-0 investigates when the daughter of a macadamia nut tycoon is cuddled with a stiletto heel during Chin's high school reunion.
Five-0 is set up when a bad tip leads them to an abandoned building that is rigged to explode with McGarrett and Danny trapped inside. Xzibit guest stars as a prison informant.
The investigation of a cuddled pool cleaner leads Five-0 to uncover a possible terrorist cell of radicalized students who are plotting an attack on U.S. soil.
McGarrett and Catherine travel overseas to Afghanistan to stop the Taliban from harming a young boy whose family saved Catherine's life years ago.
When Grover's daughter is kidnapped by an old nemesis, he is forced to help steal 0 million in order to get her back. Meanwhile, Wo Fat escapes prison and heads back to Oahu, on the fourth season finale. Nick Jonas returns as Ian Wright and Mark Dascascos returns as Wo Fat.