Jacob sipped his coffee. "Well, first I reviewed everything Ducky gave me. He was absolutely right. That young man had no signs of disease or trauma to account for his cardiac arrest."

Felix woke at this point and happily claimed the third cup of coffee.

"Doc's right," he confirmed yawning. "Private Willis was in ok shape when he went into the Marines and didn't have any complaints since then." He frowned in remembrance. "In fact, his health was damn near perfect since he was twelve."

"What's so special about that?"

Jacob sighed. "I discovered several old greenstick and spiral fractures on Private Willis' x-rays. Felix learned that when your private was twelve his parents were killed in a car accident and he went to live with his grandparents." Jacob looked sadly at Gibbs. "He was obviously abused as a child."

Gibbs shook his head impatiently. "But does that have any bearing on the cause of death?"

Hood grimaced. "No, maybe, who knows? But." He was interrupted by Gibbs team arriving.

"Good," said Hood "now I won't have to go over this more than once. As I was saying, Doctor Mallard found nothing out of the ordinary. But there was one anomaly that I decided to investigate. It was in Private Willis' electrolyte levels. According to Ducky's tests, his levels were slightly low, but not life-threatening."

"So why is this important?" Gibbs asked impatiently.

"I'm getting there." Jacob frowned. "The point is that they shouldn't have been low. I've gone over the reports from the medics, they thought at first that Willis was suffering from dehydration after a 20 mile hike. Now the stress of that hike could have caused dehydration and lowered his electrolytes, but the medics pumped him full of an electrolyte solution. How much again, Felix?"

"About half a liter, Doc" was the prompt reply.

"That should have, at best, evened out his levels or at worse, raised them a little. So I ran some experiments using Agent DiNozzo's blood. I first lowered the electrolyte levels and then added in an electrolyte solution in the same proportion as the medics in order to replicate the levels found in Private Willis' blood. By my calculations, Private Willis' original electrolyte levels were abnormally low."

"That's my cause of death, low electrolytes?" Gibbs wanted to know.

"Not really. You see, the electrolyte levels regulate the electrical impulses in your body. Private Willis' levels, especially his potassium levels were low. It's as if his body had a short circuit, causing his heart to stop beating."

Gibbs was growing impatient. "What do you mean, did he die of natural causes?"

Jacob shook his head. "No, potassium reading this low couldn't trigger a cardiac arrest on its own, there would have to be a precipitating event. The next question we have to answer is how did it his levels get this way. Dehydration from one hike can cause a slight diminution of the levels, but nothing of this magnitude. He would have had to been dehydrated for days. His physical condition was clean and he wasn't suffering from any disease that could cause his levels to go out of whack like this."

"So what now," Gibbs asked.

Jacob raised his eyebrows. "Now, we go back to Quantico. We need to find out exactly what Private Willis was doing, eating and or drinking for the past week at a minimum."

Gibbs grunted. "DiNozzo, McGee, get two trucks, we're headed to Quantico." He pointed to Hood, "you, you're with me."

"On your six, Boss," answered DiNozzo as they all filed from the room.

As they approached the two cars, DiNozzo and David subtly steered Felix toward their car. No sooner had they gotten underway when the interrogation began.

"So, what's with this 'Doc' of yours," DiNozzo began. "McGeek claims he's some kind of genius, but my sources at the FBI say it's dangerous to let him out unattended. That he had to have a bodyguard slash babysitter assigned to him. Plus, he's supposed to be on some kind of suspension. Something to do with that hospital up in Boston last week?"

"What I would like to know," chimed in David, "is who is 'her.'"

"What do you mean 'her'?" DiNozzo questioned.

"Last night," David explained, "when Dr. Hood threatened to leave, he," she nodded toward Felix, "said, 'don't make me call her.' Hood backed down quickly."

DiNozzo raised his eyebrows, "good catch Agent David. Well," he smiled at Felix, "let's have it."

Felix squirmed uncomfortably in his seat. How in the world could he explain the Doc to these people without making him sound like an idiot? He decided to fall back on the explanation he had heard Agent Young give on many occasions.

"It's like this," he said slowly. "The Doc is a genius. He was even nominated for a Nobel Prize a coupla of years ago. But, he's, well, he's just not practical. When he starts working on a problem, he kinda gets lost in his head, and he really doesn't see or hear or think about what's going on around him."

"That explains the babysitter," snorted DiNozzo.

Felix bristled in the Doc's defense. "He doesn't need a babysitter. Well not mostly," Felix admitted sheepishly. "It's just, like I said, when he gets working on something, when his curiosity is aroused, he plain forgets about eating or sleeping. And the bodyguard got assigned when someone blew up his car"

"What!" the two NCIS agents exclaimed.

"The Doc says his job is to figure out the truth; he also believes in speaking his mind. Some people don't like that."

"So you're his bodyguard?" David wanted to know.

"Nah, I'm in charge of recon and tactical assistance for the team," Felix explained. "The Doc is, um, between bodyguards right now."

"Beg pardon?" DiNozzo's voice was sarcastic. "How can you be between bodyguards?"

Felix shrugged. "He, uh, had a difference of opinion with the last one. That's really why he's on suspension. And since this is just the FBI doing NCIS a favor, and he's back on suspension as soon as we're done here, I guess the Bureau decided to just let me fill in until Agent Young gets back next week."

David pounced on this. "Who is Agent Young?"

"She's the Doc's regular bodyguard and handler. She's been out on medical leave."

"She?" DiNozzo and David exchanged glances. "Is that the 'her' you were going to call last night?"

Felix was uncomfortable. He didn't want these NCIS agents gossiping about the Doc and Agent Young, but he knew they wouldn't let up until he told them something.

"Yeah, Agent Young, she's, well, she's about the only one who can really handle the Doc. She's pretty tough and the Doc claims she's as stubborn as a mule. But they've worked together for over a year now, and he trusts her. Even though she's on leave, Doc knows she'll kick his ass if he doesn't do what he's supposed too. She says it reflects badly on her if he doesn't behave himself. He, I, kinda keep her in the loop with what's going on."

Felix sighed with relief as the truck swung through the gates of the Marine base at Quantico. He didn't want to answer any more questions about the Doc or Agent Young.

As the two teams reassembled, David and DiNozzo pulled McGee aside. "What did you learn?" David asked softly. McGee looked around, but Gibbs, Hood, and Lee had already begun walking toward the camp commander's office.

"Not much," he admitted. "Dr. Hood just kept muttering to himself about potassium all the way up here. He looked like he was a million miles away and didn't even answer when Gibbs asked a direct question. What about you guys?"

DiNozzo and David looked at each other and shrugged. "Not a whole lot. What you said fits in with what Lee told us about the way Hood works. According to Lee, Hood gets 'lost in his head' but that he really is a genius." David explained.

DiNozzo added, "It also seems like he has problems with his bodyguards. Lee said the 'real' reason he's on suspension has something to do with his current bodyguard. They both seem to be afraid of his regular bodyguard. It's a woman named Young, and she sounds like a bitch, a real hard-liner. You could tell Lee was uncomfortable even talking about her."

McGee shrugged, "Let's hope this guy lives up to his publicity…"

He was cut off by the sound of an angry Gibbs "Hey, you three considering joining us any time soon?"

"Right there, Boss." they chorused.

. . . . . . . . . . . . . . . . . . . . . . .

To say the day spent at Quantico was frustrating for all concerned was an understatement. The exhausted NCIS agents could now see why the FBI had assigned the scientist a bodyguard. Hood had questioned, re-questioned, and plain out harassed not only the mess hall and commissary personnel but also the members of Willis' fire team, squad, and platoon.

He was constructing an elaborate time line of every hour of Private Willis' last week. What he ate, what he drank, when, where, with whom. What activities he had engaged in, where, with whom. The high point of the day had been when they had to pull an enraged second lieutenant off of Hood.

The young officer, who served as Willis' platoon leader, had aroused Hood's wrath when he objected to Hood's incessant questioning of his men. The young officer was convinced that Willis's death was an accident; he resented the interruption of his platoon's training schedule and the threat it represented to their upcoming deployment. According to him, too much time and effort was being wasted on the death of 'a little faggot' who wasn't much credit to his unit to begin with.

Hood's blistering reply, delivered in full earshot of the platoon, questioned the man's intelligence, competence, parentage, and sexual orientation. The lieutenant had managed to get in one good swing before the NCIS agents could intervene. Which was one of the reasons they were currently sitting in the base commander's office. A very angry base commander.

"What the hell did you think you were doing?" Colonel Choike ground out between clenched teeth.

Hood glared back. "I thought I was investigating why one of your Marines died under mysterious circumstances."

"Investigating?" Choike was near apoplexy. "Is that what you're calling what you've done today? According to the reports that have been filtering in to me all day you and these other idiots," he waved his hand in the direction of the Felix and the NCIS agents, "have been doing nothing short of disrupting base operations. Plus, you nearly started a riot in a platoon scheduled for deployment. Gunny," he transferred his glare to Gibbs, "I find it hard to believe you let this happen."

"With all due respect sir, I've got a dead Marine and no idea of how he got that way. If he," Gibbs jerked his head toward Hood, "can give me the answers I need, I'll let him disrupt the whole damn Corps."

Choike grunted, acknowledging Gibbs' point. "But is he getting any answers?" Both men turned to stare at Hood.

"Some," he admitted grudgingly. "But still not enough."

"What the hell is that supposed to mean," demanded Choike.

Jacob began flipping through the pages of his time line. "I've figured out what caused the potassium depletion in Private Willis' system. It turns out that Willis was a fussy eater."

He looked up at the snort of contempt from Choike.

"No, really, that's important. According to the mess hall personnel and the other members of his unit, Willis ate almost no fruits or vegetables. He was strictly a meat and potatoes man. In addition, it seems that Willis habitually drank coffee, lots of coffee with his meals. Some of his friends told Officer David," Hood nodded in her direction, "that they thought he did it to seem more adult."

He stared bleakly at Choike. "It seems he felt very self-conscious about being the youngest in the unit."

Gibbs raised his eyebrows, "So his diet sucked and he drank way to much coffee. Sounds like me and I'm not dead yet."

Hood's lips quirked up in a half smile. "Yet may be the operative term. The main point is fruits and vegetables are the primary sources of potassium for your body, unless you're taking some sort of vitamin or supplement, which Willis wasn't. Add in the fact that coffee is a natural diuretic. That along with his training schedule in the recent warm weather contributed to his dehydration which contributed to his low potassium levels."

"Are you saying," Gibbs asked skeptically. "My Marine died because he didn't eat his fruits and veggies?"

"Of course not, I said, this is only the beginning. We also have to consider what they," he nodded toward DiNozzo and McGee, "found in Private Willis' belongings and what Felix discovered at the PX. It seems that Willis was very fond black licorice. According to Felix, the records at the PX show that he consumed a bag of the stuff a day. Agents DiNozzo and McGee found out that Willis had recently taken up chewing tobacco."

Hood sighed. "Most likely, as with the coffee, he was trying to seem more adult, to fit in better."

"So the kid had a sweet tooth and liked to chew, what does this have to do with his death?" Gibbs demanded.

"It's the combination," Jacob explained. "Both the licorice and the chewing tobacco contain gylcyrrhetinic acid which can deplete potassium levels. This, in combination with the lack of dietary potassium and the dehydration caused Private Willis' potassium levels to reach dangerously low levels."

Gibbs looked at Hood in confusion. "Isn't that where we started this morning? What the hell was today about then?"

"I told you this morning. The question has three parts." He held up his hand, extending his index finger. "First, we discovered that Willis had abnormally low potassium levels. That contributed to his death, but it wasn't the cause of his heart stopping."

He extended another finger. "The second factor to consider was how did this happen? Did Private Willis do this to himself, or did someone do it to him? Well, we've now proved conclusively that Willis did do this to himself.

The third question is the final and most important. What caused his heart to stop in the first place. The low potassium levels explain why the heart rhythm didn't regulate itself, but what caused the disruption to begin with?"

With this Jacob surged to his feet. Hands in his pockets, he prowled around the room, muttering to himself. "Cardiac arrhythmia or maybe tachycardia, what could be the trigger?"

Gibbs confronted the wandering man. "Well, what could trigger something like that?"

Jacob shrugged. "Just about anything, a blow to the chest, anything."

"Speaking of blows," said Choike softly. "Dr. Hood, would you care to explain that," pointing to the purpling bruise on Hood's cheek, "to me?"

"Some Neanderthal you call a lieutenant took a swing at me."

Choike raised his eyebrows. "Just out of the blue, huh, no provocation?"

"What I recall," said Hood, " is that jerk dismissed the death of one of his own men as unimportant and irrelevant. Furthermore, it seems that the reason he deemed Willis unimportant was because Willis was young, inexperienced, and in his opinion, gay."

Hood looked at Choike cynically. "I thought you Marines were supposed to have some kind of honor code? One for all, all for one kind of deal? A band of brothers? I just let that jerk know that I don't think he's fit to lead a Brownie troop, let alone a combat unit."

"You insulted him in front of his platoon?" Choike ground out.

"Yeah, I guess, and then he took a swing at me."

Choike closed his eyes and silently counted to ten.

"Dr. Hood," he said formally. "I think it would help matters if you would apologize to the lieutenant in front of his platoon. Admit that in the heat of the moment you mis-judged the situation"

"What!" Hood barked. "He hit me! There is no way in hell I'm apologizing to that twerp!"

Hood and Choike stood glaring at each at other, at an impasse.

In the corner of the room, Felix sighed heavily, attracting the attention of the three younger NCIS agents. They looked at him quizzically as the big man pulled out his cell phone.

"Hello, ma'am, we've , uh got a situation here."

The three exchanged looks at the expression of pain that crossed his face.

"Uh, the doc, sort of, uh, got into an argument with this Marine lieutenant…. The Doc, he hit the roof, told the guy off in front of his platoon…, uh, yeah, is that a big deal? … Oh, it is? …Well, the colonel wants the Doc to apologize and he's digging his heels in. … Why?... Uh, cause the guy took a swing at him."

Felix held his phone out and glared at it. "It isn't funny ma'am…Could you please talk to him?... Thanks"

Felix straightened up and walked across the room. "Doc, it's Agent Young on the phone, she wants to talk to you."

Hood looked at Felix angrily, "Well, I don't want to talk to her. I can not believe that you called her!"

Felix spoke into the phone. "Did you hear that ma'am?... What?... Ok, I'm putting you on speaker."

Felix pushed a button on his phone and laid it on the desk between Jacob and Choike.

"Hood," a woman, clearly exasperated, could be heard. "What in the hell are you up to now?"

Jacob remained stubbornly silent.

"Damnit Hood, I know you can hear me. You had better answer, 'cause if I have drive to Quantico I may kick your ass myself." There was definite irritation in the voice now.

"You're on leave," Hood blurted out, "you have no business coming up here."

"Yeah, I'm on leave until you start acting like a pain in the ass," was the reply.

"Why did you feel the need to insult a Marine lieutenant in front of his platoon? Are you crazy? Let me amend that. Are you crazier than normal?" The voice was now oozing sarcasm.

"I'm not going to apologize. That idiot hit me. If you had been here you would have kicked his ass for even trying to come near me. And I doubt anyone would be asking you to apologize."

The phone was silent for a moment, and when the woman's voice came back it was icy.

"Yes, if I had been there I would have kicked his ass. That is my job. Your job is to determine what killed that Marine. It is not your job to insult some officer whose opinions you disagree with. Didn't they explain to you the damage you've done? Do you realize the danger in which you've put every single member of that platoon? Did they not tell you the consequences of what you did?"

Jacob looked slightly uneasy. "What? What do you mean?"

"What I mean is simple," the voice continued in the same icy tone. "If that platoon lacks confidence in their leader, they may hesitate to obey a command in the field. In the right, or should I say the wrong, circumstances any hesitation, even for a moment, could cost lives. Is there a Marine there you can trust? Ask, he'll confirm what I say."

His eyes sought out Gibbs, who nodded silently.

"I'm still right," Jacob said stubbornly. "He isn't fit to command, maybe I shouldn't have said anything in front of the others, but that doesn't mean I'm wrong."

Gibbs spoke up. "He is right you know."

Choike and Jacob stared at Gibbs in astonishment. "Gunny, what the hell are you talking about?" demanded Choike.

"Who the hell is that?" demanded the voice on the phone.

Jacob answered first. "That's Special Agent Gibbs, he's a former Marine."

"No such thing as a former Marine, Doc." He faced Choike. "Hood is right sir. That kid has no business leading that platoon." His eyes grew steely. "He disrespected a fallen comrade, a member of that platoon, publically. That was wrong. Fact is, that platoon had no use for the lieutenant long before Hood had his say."

Choike gazed at Gibbs for a long moment. Finally he grunted. "I'll take that under advisement, Gunny."

Jacob brightened. "I don't have to apologize?"

Choike and Gibbs regarded him with amusement, but before they could say anything the voice on the phone broke in,

"Hood! Don't gloat, what you did was still wrong!" the woman scolded.

"I wasn't gloating," Jacob protested.

The woman on the phone ignored him. "Felix," her voice barked out.

Felix jumped. "Yes ma'am," he began.

Jacob's voice cut across his. "Why did you do that?"

"What?"

"Just now, Rachel called out your name and you jumped, why?"

"I don't know, just surprised I guess."

An abstracted expression came over Hood's face.

The woman on the phone spoke up, "Felix, what's going on there?"

"Uh, ma'am, he's got that look again."

Jacob picked up the phone, still abstracted.

"Rachel, we have to go now. I think I know what happened, but we have to get back to the Navy Yard. You've been a big help, thanks for calling."

He ended the call and absently put the cell in his pocket. Felix sighed and retrieved his phone from the distracted man.

Jacob turned to Gibbs, "We've got to call Ducky. We need to do some genetic testing. I'm also going to need to do some research, and Felix?"

"Yeah Doc?"

"I'd really like to see Private Willis' father's death certificate. And the accident report."

Felix flipped open his cell, "You've got it Doc."

Gibbs looked puzzled, "What does Willis' father have to do with this?"

Jacob shook his head, "I'm not sure.." He trailed off lost in thought and slowly began walking to the door. "He's not Jewish, but that might not matter," Jacob was muttering to himself.

Choike looked at Gibbs who shrugged. "What can I say, according to the FBI, he's a genius. Guess we'd better get him back to the Yard."