A teen girl purchases a .38 handgun from a junkie. Junior's old junkie friend Hilo told Five-0 about the sale of the gun to the girl. So Five-0 tries to locate her. The same gun was used in 1983 in an ambush of two cops with one killed. Hester, the man with the gun, made the other cop call John McGarrett. John had sent Hester away for the manslaughter of his business partner. Five-0 gets called out for a murder done with a .38, and they suspect the girl. The same gun was used in a convenience-store robbery in 2010 of which Danny gets caught in the middle. Jerry tracks down Bonnie, the buyer, at a local high school. But she and her father stonewall McGarrett and Danny. The murdered man was dating Bonnie's mother. Koa was using the same gun for target practice at a party in 2015. It was used in a gang murder later that night. Bonnie admitted to buying the gun because the man beat her mother. It's gone from where Bonnie hid it. In 2015, a detective advised Tani to get away from her gangbanger boyfriend Damien. Bonnie's father is arrested for the murder. The murdered man had stolen the gun and he and Owen wrestled over it and it went off. Adam and Tani find Bonnie's beaten mother Kiana at a friend's house. The "community gun" was linked to 14 crimes. Five-0 is connected to three of those. Hester shot John McGarrett, but he had on a bulletproof vest. The other cop shot was Duke and McGarrett saved him. Danny and Tani interrogate Maleko and he points them to the robber from 2010, now a church usher. Steve and Duke arrest Hester in California after he shoots at them.