As McGarrett (Alex O’Loughlin) hires an old friend (Treat Williams) now working as a private investigator to shadow his mother’s (Christine Lahti) movements around the island, Five-0 investigates the murder of a Hawaiian hand-to-hand combat master and cousin of Kamekona (Taylor Wily) shot and left for dead in the trunk of a car.
As Kono (Grace Park) and Chin Ho (Daniel Dae Kim) talk with the man’s daughter (Summer Glau) about why he suddenly needed a gun for his protection, McGarrett and Danny (Scott Caan) tail a tight-lipped Kamekona who refuses to explain why he provided the victim a firearm shortly before his death. Catching the abduction on video, the Five-0 Task Force tries to figure out who the kidnappers are and what they wanted from their victim who they kept for five hours while delivering an extensive beatdown before finally killing him.
After putting a little pressure on Kamekona’s niece, Chin Ho and Kono discover the victim was secretly training his daughter along with several men old school Hawaiian martial arts. The day of the kidnapping the man was forced to fight in underground traveling Mixed Martial Arts matches run by a former MMA fighter (Keith Jardine). When the victim’s daughter is kidnapped as well Five-0 has to find the underground fights before she meets the same fate. Although the team is able to find the battling young martial artist bruised but still breathing, McGarrett’s other plan doesn’t go nearly as well when his old womanizing pal begins dating his mother (who knows exactly what’s going on from the start and decides to enjoy every moment of it).