D.C. Metro Police find a Navy research scientist by the name of Sophia Glazman sitting on a park bench with a garrote around her neck. She begs them not to move her, but they eventually do. The garrote is motorized, and so when she was moved, the motor started up again, eventually decapitating her.
Glazman had been recruited to work for the U.S, and she had eventually become a U.S. citizen. When she was in Moscow, she had been best friends with another scientist by the name of Nelly Benin. After going to America, the two had remained friends but had become friendly rivals in the their race to advance their laser technology.
Upon learning that Benin had also just recently come to the U.S., Russian counselor Anton Pavlenko asked the SecNav for NCIS support in finding Benin, who they suspect had killed both Glazman as well as another scientist in Moscow. SecNav agrees and assigns the NCIS team to the case, as well as FBI Agent Leia Pendergast.
The NCIS team learns that when Glazman was killed, Benin had been delayed at the airport because of a security issue. So they knew she wasn't the killer. Bishop and McGee theorize that Benin was looking for asylum in the U.S.
A call comes into Glazman's phone - and the team discovers that the call is originating from the Liberty Square Bar. Suspecting it's Benin calling, Gibbs, McGee and Bishop had to the bar to find her.
Benin confirms to them that she would like to defect to America. She decides to head to the bar washroom before heading to NCIS. Bishop accompanies her. The real assassin - a woman by the name of Renata Atal - also enters the washroom hoping to kill Benin. Before she can do so, Gibbs barges into the washroom, wondering at their delay.
The assassin abandons her plan, but not before Gibbs realizes that she's acting suspiciously. He chases her, but she escapes by going out a door, and then using one of her motorized garrotes to lock it behind her.
Back at NCIS, SecNav orders the team to send Benin back to Russia. Pendergast is driving her to the airport when she spots a tail. It's the assassin. She drives into a garage to escape her, and Tony calls to tell her he's been following the assassin, and to wait in the car.
Tony corner the assassin in the garage but before they can take her into custody, she commits suicide by using a motorized garrote on herself.
Back at NCIS, the team takes Benin out to the garage. Counselor Pavlenko is there, waiting to drive her to the airport.
Benin objects, demanding that she be allowed to stay in America. She grabs a gun and points it at Pavlenko. Pendergast shoots her.
Satisfied that Benin's knowledge is no longer accessible to America, he departs.
Once word reaches the team that he's gone, Gibbs reveals to the SecNav that Benin is alive, and that the shooting was a ruse, all done for Pavlenko's benefit. Pendergast had used blanks.