Picking up where Season 3 left off, we find McGarrett and Wo Fat cornered by unknown assailants in a detainment facility in season 4 of Hawaii Five-0, forcing McGarrett to break the law and turn on his own in order to find a kidnapped Catherine. Meanwhile Kono and Adam's secret location in Hong Kong is compromised, and Kono and Adam fight to stay alive when their hidden location is discovered.
Episode 1
After McGarrett and Wo Fat narrowly escape from maximum security, gunmen storm Five-0 headquarters, compromising Kono and Adam's secret location in Hong Kong and forcing McGarrett to break the law and turn on his own in order to find a kidnapped Catherine.
Episode 2
As the Five-0 team members investigate a murder, they are led to a Texas ranger who came to Hawaii to look for his daughter; Adam and Kono fight to stay alive.
Episode 3
A conspiracy theorist helps Five-0 when a missing artifact is the key to solving a double murder.
Episode 4
Five-0 investigates the murder of a wedding crasher, and their prime suspect is the runaway bride. Meanwhile, Danny makes a big decision regarding his relationship with Gabby.
Episode 5
As Catherine’s seemingly harmless surveillance job takes a deadly turn, Adam considers making the ultimate sacrifice to save Kono.
Episode 6
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.
Episode 7
While working the murder 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.
Episode 8
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.
Episode 9
As Thanksgiving approaches, Five-0 investigates the murder of a secret service agent just as the President travels to Oahu. Also, McGarrett's Aunt Deb visits, bringing with her a shocking secret.
Episode 10
The attempted murder 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.
Episode 11
An investigation involving a potential serial killer puts Chin's life in danger; Grace and Danny find a mysterious puzzle box.
Episode 12
Captain Grover is aided by McGarrett in his search for a friend who has disappeared, after it seems like he's committed murder. Kono persists in her quest to find Adam.
Episode 13
Chin is questioned about his father's murder and how his relationship with Malia and her family could have adversely affected the investigation.
Episode 14
An escaped convict who wants Five-0 to prove his innocence abducts Danny and McGarrett; Grace punches a person at school.
Episode 15
A real estate agent is found dead inside the walls of one of his listings. Meanwhile, Danny's mother makes an unexpected visit and brings with her some shocking news.
Episode 16
A triple homicide is linked to a secret, downed Chinese satellite; Danny's mother goes on a ride-along with Grover.
Episode 17
A man is shot as his daughter is abducted; Danny tries to reunite his parents; Jerry finds a code on McGarrett's champ box.
Episode 18
Fan-built Episode. Five-0 investigates when the daughter of a macadamia nut tycoon is murdered with a stiletto heel during Chin’s high school reunion.
Episode 19
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.
Episode 20
The investigation of a murdered pool cleaner leads the Five-0 team to a possible terrorist cell of radicalized students plotting an attack on U.S. soil.
Episode 21
McGarrett and Catherine travel overseas to Afghanistan to stop the Taliban from harming a young boy whose family saved Catherine's life years ago.
Episode 22
When Grover's daughter is kidnapped by an old nemesis, he is forced to help steal $100 million in order to get her back. Meanwhile, Wo Fat escapes prison and heads back to Oahu.