McGarrett and Catherine head to the DMZ between North and South Korea to participate in an exchange: South Korea turns over two POWs, and North Korea returns the body of Freddie Hart, a Navy SEAL and one of McGarrett's best friends. Freddie was killed during a two man black ops mission into North Korea targeting Dark Sun military operatives, which resulted in McGarrett capturing international arms dealer Anton Hesse. As McGarrett and Catherine start the return journey to America, however, McGarrett notices that the body lacks a signature tattoo, and he refuses to leave until he can locate Freddie's actual corpse. After calling in a favor to Joe White, McGarrett and Catherine meet with ex-pat Frank Bama (ep #210), who gives them weapons and directs them to secret border crossing in to North Korea. McGarrett and Catherine track down Freddie's body, but when McGarrett discovers the Dark Sun soldiers mutilated his friend's corpse, he vows to get revenge on the man who gave the order. That man, Han Ji-woon, is now the leader of the local Dark Sun camp, so McGarrett and Catherine try to stealthily try to break into the camp to exact vengeance, but they are captured by the Dark Sun guards. After a tense standoff with Ji-woon, McGarrett and Catherine manage to get the drop on the guards, kill Ji-woon, and escape the country. Once back in Hawaii, McGarrett oversees the proper burial of Freddie's body.
Throughout the episode, McGarrett recounts the mission into North Korea that resulted in Freddie's death, which we see through flashbacks. McGarrett carries a great deal of guilt with him for not being able to save Freddie, but he hopes that retrieving his friend's body will absolve him of that.