The episode begins, a woman's having problems choosing a picnic spot, in the end she manages to find one, but it's a good thing they move because a body falls right where they were, much to their absolute shock and horror. Meanwhile, Jimmy enters the bullpen excited to show off his "so bad it's good" tuxedo and papers for the guys' sizes. He still needs to pick his best man, who hasn’t yet zeroed in on. Gibbs calls with the case and says he'll meet them there. That's because he's still at home, and both he and Samantha are on their ways out—him to the case, her to a meeting. Things are going very well for them, from the look of things. At the crime scene, they find a Chaplain Corps' coin in the victim's, Walter, pocket, with dried blood on it.
Ducky doesn't think it's his. The blood it turns out is Navy Commander Theresa Wade's, and Maria tells Gibbs that she's supposed to be on a relief mission in South America, but no one's been able to reach her for a week. Meanwhile, Jimmy's still trying to figure out his best man, and Ducky bows out of the running with the excuse "mentors make terrible wingmen." Gibbs joins them, and talk turns to the case: Walter was still alive when he was thrown from the aircraft, despite being beaten, stabbed, and shot. Ducky has sent tiny fungi from his throat to Abby; so she can investigate further. Walter had recently gone on a tour in Columbia, and of the three aircrafts in the area when he fell; Alfred Holbrook's seems to be the one they're looking for. He has a record, but when they question him, he's in a wheelchair and claims he hasn't flown in over a year and someone's setting him up; as he is clearly innocent from the looks of it.
After looking at the fungus, Abby tells Gibbs and Maria the herbicide is used only in Columbia—in the area Theresa was going to, a dangerous cartel country. Ziva's contact gets back to her, and Monique reveals that she may know how to find Theresa. Monique has heard that the cartels have taken Americans. She calls Gibbs "legendary" when Ziva introduces them; as she is clearly impressed by his reputation. Focusing back on the case, she has recovered footage of Walter with Theresa. The cartels didn't like the aid they were providing. Theresa may only still be alive because she's Navy; and hence the cartels probably haven’t eliminated her, for this one reason. Gibbs is sending Ziva to Monique, but not alone, though she wishes she was. Tony's joining her as he wants to ensure that she is safe, and Maria talks her way onto the trip, as she too is curious about the whole affair and wants in on it.
Meanwhile, Samantha shows up at NCIS HQ with a pizza box and Parker waiting in the car. Gibbs still hasn't met him. She asks about the case, and he stops the elevator with questions of his own. Though she doesn't tell him anything, she leaves him with a kiss and the pizza box—with a lead written on the inside; in a rather enigmatic fashion. Tony, Ziva, and Maria set up shop, and when Monique joins them, she tells them it's only safe for them to travel in the dark to the villages, as then they can go about their work unnoticed and without any unnecessary hassle. Meanwhile, McGee goes to talk to Manny off of the lead on the pizza box, and he runs, but Gibbs stops him with a trashcan lid, rather skillfully. He claims to not know anything about the body and is a government mule who just follows instructions.
Meanwhile, they're sitting down for a meal when Monique notices a car pull up, and then they're get down to avoid gunfire; visibly shocked and terrified at what is happening. Luckily they manage to escape unhurt. Meanwhile, Monique tells Gibbs that whoever's watching knows his people are there, and Tony wonders if Monique can be trusted, leading to an argument. Later, he joins Maria on the balcony and asks why she's really there when she could've just stayed back to help find Theresa, and there is surely more to this than meets the eye. It turns out Theresa took Maria's place when Maria had a family emergency. Manny's alibi is solid, and that leads Gibbs to question Samantha about why she led him there. She says that it got him to the CIA and thinks its possible Theresa and Walter found something they shouldn't have. She says he should bring his team home; as they might not be safe there. Meanwhile, back in the office, Gibbs puts McGee on finding out who brought their people into cartel territory, but he's held up when the files turn out to be blocked.
Jimmy asks Abby to be his best woman, and she hugs him, visibly excited. Gibbs interrupts to bring the focus back to the case; as that holds precedence over everything else at the present moment. It turns out that the weapon that shot Walter is linked to the cartel they're looking at. Monique tells Ziva that she's involved with something she can't get out of and there are people involved in Theresa's situation that she shouldn't cross; thus sending out a warning of sorts. She wants Ziva to go home and accept this is a case she can't solve, but she won't. Monique says she may end up dead, if she doesn’t give up at this point. Meanwhile, McGee has discovered that the people who guided Theresa and Walter are CIA much to their shock, and Samantha reveals to Gibbs the true mission behind the vaccinations: getting blood samples to connect DNA across villages.
She doesn't think Theresa or Walter knew; as the evidence at hand seems to point elsewhere. Monique knew there was more going on and was planning to take care of it herself. That's not happening; they're working together. The CIA agents are in a hurry to get out of there as they have been found out, but with Ziva and Monique in the back of the van, that's not happening. They reveal that the cartel used Walter as an example and a warning and the only way Theresa's still alive is if they think she has intel; thus revealing the complete game plan and their true intent. Meanwhile, Gibbs and McGee watch news broadcast of an explosion in Cartagena before getting in contact with the others. It worked, and they're bringing Theresa home.
Monique's not coming with them, and she's not telling Ziva what she's involved in; although she tries her best to find out. She does have some advice for her though: to look to herself, not others, for happiness. Samantha shows up at Gibbs' with a picture of Monique. She was hoping to speak to her because she has information she needs. While she can't stay overnight because she doesn't have a sitter, Gibbs will take what he can get at the present moment, from the look of things. The episode ends at this point.