We pick up from the end of last season of Hawaii Five-0 where McGarrett was questioning Wo Fat inside a maximum security prison and then some armed men break into the facility to kill Wo Fat. McGarrett is able to take out all the men and prevents them from killing him.
One of the men is still alive and McGarrett tries to get some answers by interrogating him. It turns out the guy he’s talking to is related to the leader of a terrorist group. They wanted to kill Wo Fat, because he helped Five-0 prevent a terrorist attack that they had planned.
That same group storms the Five-0 headquarters and is holding people hostage. Then two of the gunmen plug a device into the computer at headquarters to steal information and they destroy the computer once it’s finished.
There is a new SWAT commander Captain Grover (Chi McBride) that arrives on scene to assess the situation. One of the armed men goes upstairs and Chin sets a trap for him to take him out.
Grover decides to take some action instead of waiting for the armed men to make a move. He asks them if they want any food and finds out how many armed men are in the building including the amount of hostages.
The gunmen take some action after figuring that Five-0 is slowly taking out their men. He shoots one hostage and is about to shot one more when McGarrett and Danny show up.
One of the armed men shoots the person related to the leader of the group and then they surrender. This is odd and it’s apparent that saving him was never a priority for them.
McGarrett gets a call from the leader of the terrorist group and finds out that he has captured Catherine. He wants the members of his group that HPD just took into custody to be freed.
So McGarrett stops the SWAT truck to ensure that nothing bad happens to Catherine. Once his members are freed, the leader informs McGarrett of her location.
Chin was following them, but they noticed he was tailing them. Grover is upset with what McGarrett did and he explains to him that they had Catherine.
Five-0 finds out the group stole a news helicopter and McGarrett knows of only one place in Hawaii where they can land and take-off without drawing any unwanted attention.
They set a trap for the group by laying down a spike strip and their SUV tips over. However the leader escapes and McGarrett gives chase to stop him.
McGarrett ends up killing the leader and lands the helicopter safely. McGarrett has one more chance to talk with Wo Fat before he is taken away and asks why his mother visited him.
He says that she came to apologize for killing his father, but this seems strange because Wo Fat killed her husband. McGarrett takes some blood from him, because he has suspicions that Wo Fat could be his brother.
It seems the main reason the terrorist group wanted to breaking into Five-0 headquarters was to find the location Adam & Kono.