Halloween and a shooting have Hawaii Five-0 looking for a man carrying out experiments and turning humans into zombie-like creatures.
Catherine's surveillance job turns deadly. In order to save Kono, Adam reflects on what his best move should be.
A runaway bride is the main suspect when a wedding crasher is murdered. Danny decides where his relationship with Gabby is headed.
To solve a double murder, Five-0 gets some help from a conspiracy theorist.
Five-0 assists a Texas Ranger in finding his missing daughter when they cross paths with him during a murder investigation. Adam and Kono run into problems and find themselves fighting for their lives.moreless
Steve and Wo Fat fight to escape from the attack on the maximum security unit. Catherine is taken hostage when Five-0 headquarters is seized. Five-0 goes behind the new SWAT Commander’s back to rescue Catherine. Kono and Adam find themselves exposed while hiding in Hong Kong.moreless
Five-0 is assigned by the CIA to find a missing federal prisoner after the plane he is being transported to Oahu on arrives without him, but instead has four dead bodies. After being set up for a murder, Kono finds herself on the outs again with the police force. Steve has another surprising encounter with Wo Fat. Danny reconnects with Gabrielle.moreless
Doris needs Steve's help on a clandestine mission to take back an incriminating microfiche. Kono is in jeopardy whilst getting closer to finding out Adam's secret.
Five-0 looks for kidnappers after they discover the body of the previous victim from ten years ago. Even though it might harm what she has going with Adam, Kono asks a favor of Catherine.
Things turn dangerous for a talk show host and her crew following Five-0 around when they run into Wo Fat.
Steve reflects back on his last mission in North Korea as he and Catherine recover the remains of fallen soldier.
Five-0 must determine who killed a member of a local company that is bringing sharks in closer to shore. Steve assists Kamekona in getting his helicopter license and this becomes a hot topic of discussion.moreless
A member of a local roller derby team falls to her death in front of Dog the Bounty Hunter, as he is arresting a fugitive just a few feet away. Catherine is sent in undercover as a new member of the derby team. Steve finds out that Catherine kept a secret from him involving his mother and questions whether he can trust her.moreless
During the pro-bowl weekend in Hawaii, the team catches a case investigating a murder and finds help from Arian Foster, running back for the Houston Texans.
The daughter of a murdered Lua master comes to Hawaii Five-0 for help. Steve decides to have a private investigator keep tabs on his mother.
A man who was injured years ago begins taking revenge on the police officers who caused his injuries, including Steve whose father was one of the officers responsible for his maiming.
The team is directed to investigate when a prostitute is murdered in a Congressman's home, who is nowhere to be found. Danny has his own drama as the custody hearing regarding Grace goes to court.moreless
Chin is kidnapped and taken to the Halawa Prison, where he is dressed as an inmate. He must find a way out before his identity is revealed.
When Steve arrests a man who attempted to car jack him, he meets a young boy at the station, who peaks his interest. The boy's father is missing and Steve decides to help him, being concerned that the father may be in real trouble.moreless
A camping trip with Grace doesn't turn out as planned when an armed man takes Steve and a little girl hostage. Kono meets Adam's dodgy brother just out of prison.
While Danny gets assigned to protect a Victoria's Secret model, Max and Sabrina find themselves in danger when a bank robbery goes awry.
When a therapist's patient is murdered, Steve finds evidence that the therapist may be involved. Catherine finds herself mixed up in Doris' past, when a former target is looking for payback.
Steve attempts to arrange a reunion between his mother and sister. When a young computer hacker is murdered Hawaii Five-0 steps in.
Forced to remain completely immobile, Danny tells Steve about his toughest case when he was a cop in New Jersey while bomb techs try to disarm a bomb he inadvertently triggered.
Halloween has Five-0 investigating a ritualistic murder, with evidence the killer will strike again.
Steve's attention is divided between their current investigation into a Polo players murder and the return of his mother.
Steve and Danny take some time off to enjoy a little fishing only to find themselves stranded and facing pirates.