The episode began with Kono and Adam on the run from the Yakuza in Hong Kong. When they got away from their pursuers, Adam told Kono he needed to take care of this on his own. He said he would meet her in an hour. As Kono watched Adam walk away, he was cornered by the Yakuza and taken right before her eyes.
Meanwhile, Billy and Catherine were on a routine stakeout, which was a far cry from their usually active surveillance. They were gathering evidence for Sandra Cutler to prove her husband, John, was having an affair. They photographed John and an unknown woman at their rendezvous, then waited for things to wrap up.
After the woman left, a shooter walked onto the scene as Billy and Catherine watched. The shooter walked inside the house, up to John, and shot him. Billy and Catherine exited their car, and gunfire ensued. Both Billy and Catherine were shot. Catherine drove Billy, who was more critically injured, to the hospital, where she passed out as he was being wheeled inside.
McGarrett, back at his house, was meeting Joe about finding his mother. As the two were speaking, McGarrett’s phone rang, and he headed to the hospital. Waiting by Catherine’s bedside, McGarrett told her when she awakened that Billy had died.
Later, Catherine insisted on leaving the hospital to find out who killed Billy. McGarrett and HPD accompanied her to the scene, where they found everything wiped clean. There was no blood on the floor, and the walls had been re-painted. The paint was still wet.
Back at HQ, Chin said tire tracks found at the scene belonged to a commercial van. Catherine said the shooter they saw drove a sedan, so the cleaner must have driven the van. Chin also said Cutler’s financial records showed he rented a cabin to meet Abby Maxwell, an online companion and the woman Cutler met the night of the stakeout. Chin paid Abby a visit and found that Cutler had communicated with her through a burner phone.
McGarrett and Catherine then paid a visit to Sandra, who told them the first suspicious behavior her husband had was the encryption of his laptop. McGarrett took the laptop to be processed. He asked Joe to process this through the DOD.
Meanwhile, the burner phone trace led to a car ID, and the car was being driven as the ID was given. When McGarrett and Catherine gave chase, they discovered that the man they arrested with the car had stolen it. They also found the shooter’s body in the trunk.
Kono called Chin from Hong Kong and told him that Adam was missing. Chin tried to talk Kono into coming home, but she was determined to stay and find Adam.
At HPD, McGarrett and Catherine found out the last number Cutler called on the burner phone was not Abby’s. And, it was a number Cutler called after the shooting started.
McGarrett got a call from Chin, and he and Catherine returned to HQ for Joe’s findings. Joe found that Cutler had been downloading classified data from his wife’s laptop at work. Apparently, he had downloaded the data onto a flash drive and sold it to someone. Chin had gotten his contacts at the FBI involved, and they had found the number Cutler called to belong to one of three corporations. Catherine recognized one of the subsidiaries of one of the corporations, and it was found that the company owned the cabin Cutler had rented. The team determined the cabin to be a drop for the flash drive. They picked up the company’s owner and questioned him under the suspicion of corporate espionage and murder. He finally admitted to the cleanup of the murder scene but denied the murder, saying they cleaned the scene because they did not want to be traced back to Cutler. Theirs was the number Cutler had called from the burner after he was shot.
Meanwhile, Joe broke into McGarrett’s home and took a piece of small paper from the battery compartment of John McGarrett’s tape recorder in the toolbox labeled “Champ.”
Chin told McGarrett and Catherine that blood found at the scene of the crime showed that Billy had shot the killer. DNA matched him as Jason Kroll, a suspected hit man. Kroll’s Parole Officer had given Chin his address, and McGarrett, Chin, and Catherine followed up.
At the suspect’s house, Kroll opened fire from a locked door. After firing back, McGarrett broke into the room and found Kroll on the floor, dying. After his death, the trio examined his laptop and found an email from Abby’s office, signifying that she must have been the one who hired him to kill Cutler.
When McGarrett and Catherine spoke with Abby, they discovered she was out of town at the time of the email. The email had come from her assistant, who made a run for it. Before being taken away, he confessed his love to Abby.
The ending scenes included a service for Billy and a visit from Joe to McGarrett at Billy’s wake. Joe informed McGarrett that he had proof that McGarrett’s mother was alive and active again.