After Steve's CIA agent friend is killed, McGarrett lets himself be captured by the group he thinks is responsible and endures a torturous sensory deprivation tank to find the killer. Also, Tani wrestles with whether or not she will tell McGarrett about the murder weapon she found at Adam's house
The episode opens with an unknown person inside a sensory deprivation tank. A team, led by Wo Fat, is instructed to remove the person who is then strapped to a table. Wo Fat cuts a mask off the person's face who is revealed to be Steve McGarrett and is pronounced dead by Wo Fat. The scene then restarts however this time, Steve is removed from the tank because he is hallucinating the Wo Fat scenario.
Two days earlier Steve and Junior are digging a hole in Steve's back yard to bury the investment money from Kamekona for Steve and Danny's restaurant. The team is then called into a case when a dead body washes ashore on a beach. Steve recognizes the body as Tom Hennessy, a former friend who helped him track down Victor Hesse, the killer of Steve's father. Steve and Danny visit Hennessy's apartment to investigate; they are met by an intruder. The three engage in a fist fight who is killed in the process. Upon continuing to investigate the apartment the CIA arrive, including Steve's ex-girlfriend Greer and her partner Miller to remove anything that could compromise a case.
After an autopsy Noelani informs Steve that traces of Gutta-percha were found in hair follicles of Hennessy's eyes, ears, and nose. At the Five-0 Headquarters the team begins to put together torn burnt pieces of paper found in Hennessy's fireplace. When meeting with Greer she informs Steve that there is possibly a mole inside the CIA. Five-0 is able to place together the words "Cocoon" and "SS Arcturus". Steve and Danny find a ship by the same name in a pier near where Hennessy's car was towed. Steve infiltrates the ship and finds a cocoon-like room which holds a sensory deprivation tank.
The Five-0 Task Force devises a plan to allow Steve to be captured by the members of the ship and plant false information with the CIA mole. Steve enters the ship and is drugged, prior to passing out Greer is revealed to be the mole. Steve is placed inside the tank and moments later he begins hallucinating. During a shootout between law enforcement and the ships armed guards Steve manages to escape detainment and fights off his kidnappers. The rest of the Five-0 team shortly finds Steve and informs him that they were forced to let Greer escape assuming she took the bait.
The episode is a remake of the 1968 episode of the same name
- Kamekona Tupuola, Victor Hesse, John McGarrett, Governor Keiko Mahoe, Catherine Rollins, Lynn Downey, Adam Noshimuri and Noriko Noshimuri were all mentioned, but did not appear.
- It is reveled Steve McGarrett broke up with Lynn Downey.
- Steve McGarrett had a short relationship with Greer "a long time ago... right after I got my trident. It was before Catherine."
- There is a quick flashback to 2001.
- Kamekona Tupuola investing in McDanno's resturant is brought up. 
- Steve's father's murder at the hands of Victor Hesse was mentioned. 
- Tani Rey talks about finding a gun and Adam Noshimuri place  and his pending link to his sister's death. 
- Steve's dealing with Russian spies months earlier is mentoned. 
- Steve McGarrett nose was bleeding in the hotel room, after they answered the door the blood was gone.
- CIA agent Tom Hennessey
- Steve McGarrett killed 2 people 
- Danny Williams killed 3 people 
- Lou Grover killed 2 people
- Tani Rey killed 1 person
(seeing Steve & Junior digging a hole)
Tani Rey: Well isn't this cute? And suspiciously felonious.
Junior Reigns: (laughs) I see someone's been using their word- of-the-day calendar.
Tani Rey: What's wrong, Eddie? They're not letting you dig?
Steve McGarrett: It's a long story.
Tani Rey: Is it? Well, I got time. All I have to do is watch two sweaty men dig. Unless you need help?
Steve McGarrett: Oh, no, it's all right. We got Danny and Grover coming over in a couple of minutes.
Tani Rey: Do you?
Steve McGarrett: Yeah.
Tani Rey: Okay. Like, now I feel left out. #Offended. #WomenCanDigToo.
Steve McGarrett: Book him, Danno.
Danny Williams: Hey, I-I'd like to do that, but he's he's clearly dead.
Danny Williams: Place got more traffic than Kanye's Twitter feed....I'll explain to you who Kanye and what Twitter is later, all right?
Steve McGarrett: You're stupid.
Danny Williams: You're stupid.
Steve McGarrett: Any idea what he's doing in Hennessey's apartment?
Agent Miller: Well, if I did, I'd be guessing.
Danny Williams: That was almost convincing.
Agent Miller: Excuse me?
Danny Williams: You know what he's doing here, right?
Agent Miller: Calling me a liar?
Danny Williams: You guys are all the same, you know that?
Agent Miller: How 'bout you guys take a walk and the agency takes over from here.
Steve McGarrett: Excuse me? You-you giving out orders now? Is that it?
Agent Greer: Everybody knows Steve McGarrett only takes orders from the governor and God. And on occasion, even they have trouble.
Steve McGarrett: It was right after I got my trident. It was before Catherine. So it's history. It's ancient history.
Danny Williams: You don't have to justify anything
Danny Williams: How many dates you been on since you broke up with Lynn?
Steve McGarrett: Please get in the car.
Danny Williams: Zero. Zero. Zero.
Steve McGarrett: Oh, yeah? Look who's counting.
Danny Williams: I'm-- What am I counting? There's nothing to count. Zero and zero is zero. There's no-no math.
Steve McGarrett: Forget it.
Danny Williams: Okay? I don't got to use my fingers. Zero is zero.
Jerry Ortega: I'm worried you're gonna come back and kill one of us.
Lou Grover: Jerry!
Danny Williams: Look at me, look at me. You all right? What's my name, huh? What's my name?
Steve McGarrett: ... Danny.
Danny Williams: Good, good. Good. How long have we known each other?
Steve McGarrett: ... 50 years.
Danny Williams: 50, that's not funny.
Steve McGarrett: Feels like 50 years.
Danny Williams: That's not funny. I'm trying to be serious here. Okay!
Steve McGarrett: It's gonna take more than a little brain scrub to make me forget you, pal, okay?
Danny Williams: You're not being genuine. You certainly didn't say it with any sort of affection towards me.
Steve McGarrett: I got an idea.
Danny Williams: Okay.
Steve McGarrett: Why don't you throw me back in there until I actually do forget you.
Danny Williams: Why don't I let you drown next time? How about that?
- This episode titled "Cocoon," is a retelling of the original series' pilot episode and it was written by the late Leonard Freeman, creator of the original "Hawaii Five-O."
- Despite being credited, Ian Anthony Dale, Dennis Chun and Taylor Wily do not appear in this episode.
|Steve McGarrett||Alex O'Loughlin||A former Navy SEAL and the leader of the Hawaii Five-0 Task Force.|
|Danny Williams||Scott Caan||2nd-in-command of the H50 Task Force and Steve's partner.|
|Lou Grover||Chi McBride||Former leader of the HPD SWAT, and newest member of H50.|
|Jerry Ortega||Jorge Garcia||A conspiracy expert and an associate of the H50 team.|
|Tani Rey||Meaghan Rath||Former HPD cadet, who was recruited by H50|
|Junior Reigns||Beulah Koale||Former Navy SEAL and turned into Five-0 Task Force|
|Dr. Noelani Cunha||Kimee Balmilero||Medical Examiner for the Hawaii Five-0 team.|
|Wo Fat||Mark Dacascos||A crime boss targeting Shelburne who is Steve's mother, Doris.|
|Agent Greer||Rochelle Aytes||CIA Agent, and had a short fling with Steve many years ago.|
|Agent Miller||Jack Coleman||CIA Agent, and partners with Agent Greer|
|Kang||Roger Yuan||Chinese spy, killing CIA agents|
|Jonathan Kray||Lamont Thompson||Chief of Pacific Operations and Counter intelligence|
|Rosemary||Susan Park||Hotel Owner|
|Tech||Erik Chang||Kang's technician|