A gunman armed with a bomb takes a city bus hostage shooting a cop. Callen sorts through the contents of Katya's safe-deposit box. Kensi attends an adoption orientation session. Gary DeMayo is the gunman. He insists that his late daughter Kara be cleared of war crimes. Sam and Roundtree meet LAPD Captain Maya Lopez. Sam asks to negotiate with DeMayo after SWAT is pulled back. DeMayo believes his daughter didn't commit suicide but was murdered. Callen and Deeks question DeMayo's wife Rachel. Sam sends in Roundtree posing as a reporter in exchange for the injured cop. Callen asks Rachel to go to the scene and talk with DeMayo. The adoption speaker attempts to calm Kensi. The name Lawrence Kerr pops up in Kara's notes. Kerr was in Afghanistan at the same time as Kara. While Rachel distracts DeMayo, Roundtree sneaks a peek at his bomb but gets caught when SWAT moves closer. DeMayo's bomb is viable. Kerr tries to run when Callen and Deeks go to question him. Kara bought the gun with which she was shot so her death is a suicide. Sam relays that information to DeMayo. Kerr drugged Kara so that he, his boss, and two others could steal the seized weapons cache. DeMayo sends everyone off the bus. Roundtree attempts to wrestle the detonator away from him when he refuses to leave. A sniper starts shooting at the bus. Kerr's missing boss is the shooter. Sam runs to the bus with SWAT shields. He covers Roundtree and DeMayo and they all just get away before the bomb blows up. Callen takes down the boss on a rooftop. DeMayo is arrested. Sam tells DeMayo that government contractors stole and sold the weapons. Kensi and Deeks debate adoption and fostering. Kilbride gets Kara's name cleared.