The long dead body of a Navy Lieutenant is discovered. The body suffers from deep stab wounds and there are fingers missing. This leads the team to Celia Roberts who is a prostitute that was guilty of two similar murders years ago. She is sentenced to 175 years for her crime. McGee goes to the prison to try t o get a signed statement from Celia and while he is there but prison riots cause him to be taken hostage by the prisoners. Ever since one of the guards, Trimble, was murdered, the other guards started to abuse the prisoners and they were using McGee as a hostage to negotiate with the prison warden for them. The warden agrees to have NCIS look into the case and punish only the person that is responsible. This task seems to be hard for the team as they look for a killer in a place where a plethora of killers reside.
It turns out that the dead guard was poisoned with antifreeze and even though he was stabbed, he was going to die anyways from the poison. They find a match when they test the prison sheets and find that they belong to one of the inmate's daughters. It turns out that Trimble was interested in the girl, Zoe Bellows, when she came to visit her mother and he threatened to kill her mom if she did not have sex with him. He also drugged her up and that's when the inmate started to poison him with the anti-freeze. Since Sharon, Zoe's mom, only had one year left in prison, Celia takes the blame for the crime and says that she killed Trimble. She wants Sharon to still be able to go home and be with her family. She also confesses to the death of the murdered Navy Lieutenant.