Abby Dunn is a detective from San Francisco, and allegedly looking to start up a task-force like Hawaii Five-0 Task Force. It, however, turns out that Abby is an Internal Affairs Officer working as a mole for Rex Coughlin's brother, Robert Coughlin. She is the current girlfriend of Chin Ho Kelly.
In Piko Pau 'iole, Abby is seen getting sworn in by Steve at headquarters and given a temporary Five-O badge. After getting her badge, Steve takes her to the main area and introduces her to the rest of Five-O. Steve explains that Abby is a detective from San Francisco, that plans to start a task force similar to Five-O in San Francisco and she’s going to be with them for a few weeks.
Abby is with Chin as they investigate the murder of 5 Chinese arm dealers.
In Hana Keaka, Abby is with Five-O when they go out to the pig farm crime scene. She gets to witness Max’s unique technique when dealing with bodies. She is also there when Five-O goes through the student rating of Professor Thomas.
Abby accompanies Steve to meet with Max in the morgue. Max apologizes for not being introduced earlier, but Abby says it’s fine - as Max was elbows deep in entrails at the time. When they find out they as going to have to wait for the pigs to pass their evidence, Abby says she’s glad she a vegetarian.
Abby and Chin set Jerry up to babysit the pigs. As they leave, Chin opens Abby car door. Abby is shocked and explains that no one has ever opened the door for her. Chin is shocked and asks not even on a date. Abby says no, Chin says that he must have just been raised as a gentlemen.
Back at headquarters, Abby and Chin have looked into the nail salon business Professor Thomas had and explain to Steve how they believe it to be a front for something illegal. They also found a student of Professor Thomas was working there and pull up his class schedule, Steve looks at his watch and says he knows where he might be on a Friday night.
Abby lets Steve know that HPD searched the crew’s hangout but they didn’t find anything.
Chin walks in on Abby still working at headquarters, he asks her what is she still doing there. Abby says she’s filling out her daily report for S.F.P.D. to prove that she’s actually work at Five-O and not hanging out at the beach all day. Chin notices that she looks uncomfortable and says she’s welcome to use his office. Abby thanks him when he sets her up and he wishes her a good night as he leaves.
In Ka Makau kaa kaua, Abby is at Steve’s place, with the rest of their friends, as they watch pre-fight weigh in with Devon Haynes and Luke Nakano. Abby welcomes Max when he arrives late, said she didn’t know that Max was Jewish.
Abby and Chin meet Kono and Adam after his last meeting with his lawyers. Kono explains that Adam is going to jail to for 18 months. Abby asks when does Adam have to surrender himself, Adam says the next day.
Abby and Chin, make their way to Max’s morgue. Max shows them his findings, Abby notices that both of the victim's eye sockets were completely shattered. Max then shows them some colored glass and Abby notices that the glass color, bright orange, is very distinct.
Abby and Chin then go to interview the bartender at The Coral Point. After the bartender tells them that their victim went into the back alley and never came, they go and have a look. Abby and Chin find their primary crime scene, blood and shattered glass everywhere. They call in CSU to process the scene.
Back at headquarters, Abby explains that they found a fingerprint on the $100 bill, that places the money from a stolen armored car heist.
Abby watches Steve drag around their suspect in the ocean behind a jet ski. Abby asks Danny if this is how Five-O interprets immunity and means. Danny says no and that what Steve is doing, is all Steve as he’s not patient when getting information from people. Danny explains that what Steve is doing is pretty mild compared to other things he’s done, Danny then cautions Abby about bringing Steve’s techniques to San Francisco. Abby laughs and says she’s agrees.
At the fight, Steve sends Abby to the control room to get eyes on their suspects. In the computer room, Abby lets Chin know that one of the staircase alarms has been set off, she tells him to be careful when he goes to look. She then lets Grover where to go, as well as Steve. She hears shots fired on Chin’s comlink and rushes to his position with her gun drawn. Abby finds the gunman down and Chin is okay.
In Ua Ola Loko I Ke Aloha, Abby wakes up naked, covered in a bed sheet, in a hotel room with Chin. They have conflicting stories on how they ended up there, Chin then says he could just go and pull the security cameras for proof. Abby says okay and kisses Chin again, she tells that he could do that, or he could join her in the shower. Abby drops her bed sheet and Chin says he can look at the footage any time and goes to follow when his phone rings.
Abby is at the crime scene with the rest of Five-O, Chin and her go to speak to the other kids at the camp. Abby and Chin meet Steve at the crime lab to go over the ballistic evidence with Eric. They then go visit Jerry when he has information on their case. Abby is there when they identify the body in the bunker.
Steve, Chin and Abby watch as the bomb squad attempts to disarm the stolen bomb. Once it’s disarmed the three of them search the van. Abby finds the rest of the bones from the bunker and the fired weapon. Later in the day, Abby discovers the identity of their shooter through next of kin.
In Hoa 'Inea, Abby and Chin have a romantic date planned, however when comes to the after dinner activities Abby tells Chin that she can’t go through with it and leaves the hotel room in a rush. Chin chases after her, trying to get an explanation but just misses her as she gets into the elevators and leaves the hotel.
The next day Abby calls Chin to apologize for her behavior. She tells that they never spoke about where their relationship meant or where it was going. She didn’t expect to feel the way she does, but she really likes Chin. Chin says it’s okay and she doesn’t have to explain, but he’d much rather have this conservation in person. Abby says she’d like that but unfortunately she’s back in San Francisco on something work related. She then asks Chin if she’ll let her make it up to him when she gets back to the island, Chin says maybe he will. However when they hang up area that Abby is in shows that she is still in in the island.
In Ke Koa Lokomaika'i, Abby is there when Danny and his mother are pulled in for questioning by the FBI about Danny’s brother, Matt. When Danny figures out that the questions aren’t really about Matt and are instead about Five-O, Abby is shown behind the two-way mirror. She’s tells her boss that this line of questioning isn’t going anywhere. Her boss replies that Five-O has crossed the line before and when they do again, Abby just needs to be there when it happens. Abby nods and says yes sir.
In Waiwai, Abby is at Steve’s house with the rest of Five-O as they discuss the man that is after them, Robert Coughlin, brother to murdered IA officer Rex Coughlin. Five-O explains who Rex was to Abby and what happened to him by Gabriel. Abby looks uncomfortable when Steve says they need to find who is working for Robert and reporting to him.
The next day, Abby meets with Robert, he tells her they weren’t supposed to meet for another 72 hours. Abby says it couldn’t wait, Robert bites and asks what’s going on. Abby tells Robert that Five-O knows about him, he doesn’t seem fazed and says that was always going to happen, the important thing is that Five-O doesn’t find out about Abby. Abby says they don’t, but they’re smart and they’ll figure it out soon enough. Robert points out they’ll only find out if she slips up, but he has faith that won’t happen.
Robert tells her nothing changes and she has to just keep doing what she doing, sooner or later they’ll get something solid on Five-O. Abby disagrees, saying she’s been undercover for months and she hasn’t seen anything that warrants the disbandment or indictment of any members of Five-O.
Robert says that Five-O have operated by their own rules for too long and that leads to gross misconduct. Abby says she hasn’t seen that, Robert then asks if she’s sure her relationship with Chin isn’t clouding her judgement. Robert says he knows it’s gotten personal. Abby then says if he felt that way, why didn’t he pull her out, Abby then figures out that Robert also has someone watching her at all times, so if she withholds intel Robert will still get it anyway.
He tells her that once it got personal, he had no other choice. Abby then tells him that the operation is a witch hunt, he’s looking for anything to bring down Five-O and avenging his brother. Abby tells him she’s not going to be a pawn in a personal vendetta. Robert tells her she’s forgetting her place, as she’s not the one calling the shots. He tells her that she’s going to go back to Five-O and she’s not leaving until they get something on Five-O.
Abby then asks what happens if she refuses, does she get written up for insubordination. Robert tells that she works for him, if she’s doesn’t do her job, she hands over her gun and badge.
That night, Abby walks into headquarters and goes to see Chin. Chin asks if everything is okay, as he left her a few messages. Abby apologizes for not being there on the case, Chin says it’s fine. He then asks again if everything is okay, as he can see that something is bothering her. Abby says no and that she has something she wants to tell him.
In Kanaka Hahai, Abby stands at the same location she meet with Robert, see looks at her S.F.P.D badge before throwing it into the ocean.
After that, Abby is back at her hotel, packing her bags. She gets a knock on her door, she looks through the eye hole before opening it. On the other side is Steve, she fearfully lets him in and tries to justify her snitching and treachery. Steve tells her that he understands that she was just following orders. She tells him that if she returns to S.F.P.D they’ll see what she did as an act of insubordination and she’ll be working patrols for the rest of her career.
Steve tells her that them she’ll just have to stay here and work for Five-O and there is someone that would really like her to stay. He opens the hotel door to reveal Chin standing there, Steve then leaves the two of them to talk. As Chin enters, Abby tells him that she’s sorry.
Abby and Chin Steve meet at Maunakea Marketplace, Abby says that Chin says they caught a case and she wants to pitch in. Abby helps Steve and Chin interrogate the local fish seller.
Abby is there when Five-O arrests the slave laborer. Later in the day, Abby and Chin reunite Edward Torres with his wife and child. After they leave the family to be alone, Abby and Chin talk. Abby tells Chin that she decided that she’ll be sticking around for a little longer. She understands that things may be difficult between the two of them because of her previous assignment but she likes it here and Chin is part of the reason she wants to stay. Abby continues to beg him, and Chin silences her with a kiss.
In Pilina Koko, Abby and Jerry are eating ice cream in the middle of the night at Chin’s place. They manage to wake up Chin, when they offer him some ice cream, he just says he’s getting a drink and then going back to bed. On his way back from the fridge, Abby begs him into having a couple of spoonfuls of the treat with them. When he sits down at the table, Abby offers her spoon to him.
The next day, Abby and Chin ring Steve to tell him that they have the phone number of the thief and text Steve the details. Steve thanks them and they hang up. Abby is with Five-O as they uncover the truth about Sara’s parentage.
As Chin is getting airlifted to the hospital, he whispers into Abby’s ear about the bracelet that Sara was wearing and it’s importance. Abby tells the rest of Five-O that Sara’s bracelet could have a tracking device in it. Steve tells her to contact all security companies that do GPS tracking on children. Abby is there when Sara is rescued.
In Pa'a Ka 'Ipuka I Ka 'Upena Nananana, Abby joins Chin in the shower and tells him that he did the right thing, Child Services will find Sara a good home.
When Five-O is called to the abandoned warehouse that Gabriel has been living in, Steve tells Abby to guard the door in case Gabriel doubles back.
Abby is taken out by out of Michelle Shioma men. The man uses her earcomm to listen in on and find out Five-O’s position. When he asks what to do with Abby, he’s told to get rid of her.
Abby manages to escape, steal a motorbike and save Grover from his ambush.
Abby then uses Grover’s earcomm to speak the rest of Five-O. Chin is glad to hear her voice, she tells them that Grover and her are okay but SWAT got hit pretty bad. She then asks if they’re okay. She tell them that Grover called for backup and an ambulance, Danny tells her that they think H.P.D. has been compromised. Steve then tells her he needs her to reach out to Robert Coughlin, to see if he was investigating any dirty cops with ties to Michelle Shioma. Abby tells him that she doesn’t think Coughlin talk to her but she’ll give it a shot. She then passes the earcomm to Grover and rides off on the stolen motorbike.
Abby meets Coughlin at Kakaako Waterfront Park, Coughlin tells her that she has 5 minutes. Abby explains that they think Michelle Shioma has a mole in the H.P.D. and needs to know if he is looking at anyone connected to her. Coughlin tells her that he sent her into Five-O to help him take them down, not to become one of them. Abby tells him that they have Gabriel in custody, Five-O was extracting him when Shioma sent in a team to assassinate him.
Abby tells him that they are literally under attack as they speak, Coughlin asks her what the hell is she doing here then. Abby says she trying to save her friends. She says as they don’t know the ID of the mole, they can’t call for backup or who to trust. That’s why she needs his help.
Abby tells Coughlin that if ever wants to see Gabriel stand trial for the murder of his brother, he’ll give her a name. Coughlin tells her to give him 30 minutes and he’ll get her a name. Abby thanks him and drives off.
Abby is back at headquarters, she has Duke on the phone. She asks if Duke is still on Shima, he says he is. Abby tells him to call her if she leaves, he says he will. Abby then asks Jerry and Max how are they doing. Jerry explains that they won the firefight.
Abby’s phone rings, it’s Coughlin and he gives her a name, it’s the call dispatcher at the police department. Abby and Coughlin interrogate the dispatcher at headquarters.
- Is a vegetarian.
- First introduced as Inspector Abby Dunn 
- No longer an acting member of the Hawaii Five-0 Task Force but a full time officer for the HPD. 
- Chin Ho Kelly was offered a position to start his own Task Force in San Francisco with Abby. 
|Mai ho`oni i ka wai lana mâlie||Lehu a Lehu||Ua 'o'oloku ke anu i na mauna||Ka Papahana Holo Pono||Ka 'alapahi nui||Na Pilikua Nui||Na Kama Hele||Piko Pau 'iole||Hana Keaka||Ka Makau kaa kaua||Kulean||Ua Ola Loko I Ke Aloha||Umia Ka Hanu|
|Hoa 'Inea||Ke Koa Lokomaika'i||Ka Pohaku Kihi Pa'a||Waiwai||Kanaka Hahai||Malama Ka Po'e||Ka Haunaele||Ka Pono Ku'oko'a||I'ike Ke Ao||Pilina Koko||Pa'a Ka 'Ipuka I Ka 'Upena Nananana||O Ke Ali'I Wale No Ka'u Makemake|
|Makaukau 'ce e Pa'ani||No Ke Ali'i' Wahine A Me Ka Aina||He Moho Hou||Hu a'e ke ahi lanakila a Kamaile||Ke Ku 'Ana||Ka hale ho'okauweli||Ka makuahine a me ke keikikane||Hana Komo Pae||Elua la ma Nowemapa||Ka Luhi||Ka’ili aku||Ka 'Aelike||Ua ho'i ka 'ōpua I Awalua|
|Ka laina ma ke one||Ka Pa'ani Nui||Poniu I Ke Aloha||Hahai i nā pilikua nui||E mālama pono||Puka 'ana||Huikau nā makau a nā lawai'a||Ua malo'o ka wai||Waimaka 'ele'ele||Wehe 'ana||He ke’u na ka ‘alae a Hina||Ua mau ke ea o ka 'aina i ka pono|