A young gang member is trying out weapons from another guy. He shoots and tries them out and gets excited and to be a better shot with each one. When he is handed the semi-automatic gun, he shoots up a mattress, then fires up at the ceiling. The body of a dead marine comes crashing down through the the skylight and hangs by a rope. The bigger guy scoots and tells the kid to disappear as well, but he stands there for a second.

Back in the squadroom, Tony and Ziva are exchanging their usual barbs. McGee announces to Tony that he had received a phone call for him. Tony asks what was the number but McGee can only remember that it was some girl called Melinda. Tony tries looking up his black book for listed Melinda, and wonders if it was the one he met while dog walking. Ziva is interested as to how many listed Melindas there are in Tony's phone list and McGee reminds him that Tony does not own a dog. Gibbs comes in and they got a call to Liberty Heights. Upon arrival, Ziva points out the 9MM shells and .357 Magnum holes in the wall and the use of the semi-automatic weapon. They notice the tattoos that the dead marine, Emelio Salazar, was having removed on his arm. As McGee is trying to make out what the tattoo was, Gibbs points to the wall and says "it was that." McGee reads aloud. "PC's."

Up on the roof, Tony finds bloodied handcuffs and takes photos of them. He also notices skin on them and they realize Salazar had been on the roof, handcuffed for a while. They move a blanket and see a number written in blood. They realize it's not a phone number but a Marine Service number. McGee offers to run it but Gibbs tells him not to bother, it's his.

Back at the squadroom, Tony fields a phone call from Vance for Gibbs. When Gibbs arrives, he passes on the message. Gibbs asks about Salazar. The team informs him that Salazar had only been in the military for 4 months. Prior to that, dating back to age 12, he had a criminal record, all gang related. Gibbs comments that Salazar survived 6 years on gang streets but couldn't survive 4 months in the Marines.

Tony and Ziva go to where Salazar was stationed and question his supervisor, Marine Staff Sergeant Vincent Medina. As they walk into the firing range, Ziva mentions she hasn't been there in a while. Medina tells them to be quiet on the range. Tony loudly yells that he's very talky and he's got a badge and shows it to Medina. He tells him they can talk there unless Medina finds them somewhere quiet. Medina calls for quiet on the range and asks the marines to leave. When they do, Tony and Ziva inform him of Salazar's death and question him on Salazar. Medina has very little to offer them. Ziva remarks that Medina is using a 9mm Beretta and he offers to let her fire it. Ziva takes the gun into the gun range and fires one shot. She hands it back to Medina and remarks she doesn't like it. Medina remarks that most women don't like that weapon. Ziva tells him she prefers a SIG and then informs Medina the sights on his weapon are off a bit. Tony laughs and says she's right as he hands Medina the target silhouette Ziva had fired at and there's one shot to the head, just slightly off-center. Tony laughs and walks off.

Gibbs calls in Mike Franks to help him with the investigation without telling Vance. Vance is already suspicious about Gibbs not returning his calls and confronts him at the same time Ducky does. Ducky is, however. able to tell him that the machine gun wounds were post mortem whereas the single shot that went through his ribs is what killed him. That bullet is with Abby, who manages to tie it with a suspected gang related gun, which is licensed to a PC member called Popeye. (?) Gibbs sends Ziva and Tony to bring him in. When they reach there, the 3 gang members scoff at Tony and Ziva but Popeye is tackled by Tony while running away and the other two find out why Tony mentioned that he feels safe having Ziva as her bodyguard.

Franks had Tomas' mom (Rose) brought to America a long time ago. The neighborhood is now all gang. They find out she died of cancer 10 years ago. Gibbs and Franks go to speak with Tomas and have a nice chat with Kari Coleman, who is legal guardian to many of the kids in the gang; she's trying to keep them on the straight and narrow. Tomas arrives and has no idea what has occurred. Back in the interrogation room, Gibbs and Franks talk with Tomas, who says he was Cape Haterous for the past 48 hours. Tony and Ziva note Gibbs is going pretty light on Tomas. When faced with Gibbs' secruity number and his blood on the roof, Tomas denies killing PFC Salazar and maintans he was not there, even under scare tactics from Gibbs and Franks. They both recognize he is scared and hiding something.

In the next interrogation room, Gibbs and Davis interrogate Popeye, who smugly responds they've got nothing on him. Popeye confesses to killing Salazar but they don't believe him. They know he is lying when he says he shot Salazar in the head. Franks opines he taking the credit to elevate his street stature.

McGee traces call and finds one number that keeps popping up from outside the hood that called almost every member of the PC gang: Vicente Medina. It turns out he was not just recruiting from the PCs, he was a PC member.

Vance shows Gibbs he has Gibbs' marine file and asks his permission to read it. He's looking for info on what happened in Columbia 18 years ago. Gibbs wishes him happy reading. Throughout this eposide there is a implication that Gibbs is the father of Tomas.

Gibbs and Franks interrogate Medina, who denies killing him. Medina does not have an alibi as he was at home watching tv. He joined the marine corps to escape from the street life and then returned to the hood to convince others to make something of their lives. Ziva interrupts with the results from a facial recognition search from a picture which shows Medina in a cafe last night. It proves he could not have killed Salazar. So why is he lying? He went to visit his son and his wife doesn't know he has a kid. Franks says to Gibbs, "I guess we all make mistakes, huh, Probie?"

Franks summarizes in the bullpen - ignoring Tony and Ziva's questions about what happened in Columbia 18 years ago and Gibbs' involvement. When Gibbs walks in, Franks requests to interrogate Medina seriously. Gibbs says he let him go so they could follow him. Ziva and Tony are to go up to MTAC with McGee. Franks and Gibbs have a showdown in the elevator about Rose not wanting Gibbs to know because she didn't want to complicate his life while he was trying to recover from the death of his wife and daughter. Franks states "I guess she didn't get her wish after all." The conversation implies Gibbs is Tomas' father.

Using the GPS signal from Medina's cell phone, Gibbs and Franks are in pursuit of Medina until McGee advises he has gone to Quanitco. Gibbs U-turns in the opposite direction, heading to where Medina was before. Meanwhile, Tony is bossessing with McGee and David about what occurred in Columbia 18 years ago. Vance comes in and states it is classified. Vance asks for information but Tony refuses to answer and busys himself with inspecting his fingernails. McGee and David answer his questions and he requests a call to base security when he is told Tomas is a guard at the armory and Salazar was also. Vance advises Gibbs that 4 crates of M4 assault weapons are missing. Thomas enters the crime scene wheeling 4 crates as Gibbs peeks around the corner at him. Tomas tells whoever ordered the weapons to come and get them. Gibbs directs McGee to record the secruity camera pointing at Tomas. The 2 gang members Ziva "subdued" arrive - she comments "I should have hit them harder."

Medina suddenly shows up pointing a gun and yelling "freeze, freeze! Put your hands in the air! You thought you were going to use marine guns to kill my friends!?!" Gibbs and Franks move closer. Shooting starts; Medina is wounded in shoulder, Tomas is unhurt, and the 2 others are dead - 1 by Franks. Vance calls but Gibbs tosses the phone to Franks, who shuts Vance down. Medina confesses it was him who ordered Tomas to take the weapons off the base. Tomas did so because they threatened everyone he loved if he did not. They killed Salazar in front of him to show their seriousness. Medina wanted to handle it: "we take care of our own." Gibbs says these guys are just the hired help.

Ziva interrogates Tomas with Coleman watching distressfully. Gibbs and Franks stress he is going to prison. She confesses the guns were for the PCs as protection/deturrants. She is led off in handcuffs.

McGee presents Melinda's number to DiNozzo - she is from his dentist's office. Suddenly DiNozzo has a realization and he questions Franks, asking if Gibbs is Tomas' father. Franks does not answer.

Gibbs give Tomas his orders. He is shipping out to Afghanistan. Tomas tells Gibbs what his mother told him happened 18 years ago. Gibbs flashes back as he does so. Gibbs is the reason Tomas became a marine. Gibbs answers his unasked question about whether Gibbs is his dad. Gibbs and Vance have a convesation in which Vance recaps the Columbia assignment and knows the answer, too.