Night had fallen, the building had emptied of most of the agents, and the remaining few huddled over their computers in a daze as MacGyver finally staggered back into the squad room. The lab coat he'd borrowed from Abby was now gray, heavily streaked, and liberally charred with burn marks. "If we keep going, we're gonna make a mistake that will blow the place up," he admitted as Gibbs, DiNozzo, and McGee looked up at him. Crossing the bull pen to collapse into Bishop's empty chair, Mac leaned backwards and stretched. "I forgot how much energy Abby has," he said with a tired smile. "That girl wore me out!"

Gibbs snorted once, then made a gesture that demanded more information.

"We had a pretty good Special Effects show going on down there. He's got the makings of a pretty dangerous, highly untraceable grade of explosive."

"That's not good," Tony observed.

Mac blinked heavily to shake off his fatigue. "Agreed. But as crazy as that mixture is…" He shrugged. As Gibbs repeated his 'get on with it' gesture, Mac could only spread his hands in confusion. "We're missing something," he condensed.

"You were going on about the white powder?" Gibbs prompted.

For the benefit of Tim and Tony, Mac decided to back up. "Abby and I only used the chemicals she found, in the amounts purchased on the invoices you guys found. We started with the exact products purchased, then branched out a little. When we put together a certain combination, using the dish soap, it left behind a white residue that is stable by itself, but incredibly volatile when mixed with an accelerant…and impact, apparently… Oh, yeah, and Abby's going to need the floor replaced by her centrifuge," he admitted with a wince.

"You destroyed her floor, and you still think you're missing something?" Tony asked.

"The place is still standing, right?" Mac pointed out. "We had exact duplicates of what we learned Salazar's companies bought. Even if we'd have mixed everything all at once, the explosion might have gutted the two lowest floors but it wouldn't have taken this place down. Hence, we're still missing something." He soldiered on over the surprised looks everyone was giving him. "I tried to guess what our missing ingredient was, and think I might have gotten close. Tim, if you'd be so kind, I'd like you to check to see if any of Salazar's companies bought any of these things."

McGee watched expectantly as MacGyver scribbled a short list of products containing the mystery ingredient, and as the list drew to completion, he brought up the proper program on his computer. He paused for a moment as he realized Mac had not yet moved out of Bishop's chair, and when he looked up, he saw the exhausted man in the middle of an intricate fold in an impressive paper airplane. "Sorry, McGee, but I'm too tired to stand," Mac apologized as a quick flick of his wrist sent the plane soaring across the room.

Tim grinned at the unorthodox delivery method as the plane landed on his desk. He unfolded the plane, making a mental note to reverse engineer the craft later on so he could reproduce it, then started tapping away at his computer. "I bet Abby's on Cloud Nine right now, having had you in the lab with her all day."

"Good times," Mac agreed after hiding a yawn. "I remember when I could spend three days straight in the lab, working on a project like this. Pete would have food delivered to me, and if I didn't get around to eating it, he'd come down and force me to take a break himself." He stretched again. "Gotta admit, I'm tired now!"

"Right after a three-day solo job that didn't allow you a break, you headed out for a two-day excursion into the wild," Tony reminded him.

"And didn't get a whole lot of sleep while we were out there, either," Mac agreed. "Bishop wasn't too comfortable, and made sure we knew it." Pushing that thought aside, Mac reached for his laptop and flipped the lid up. "When was the last time you heard from my office?" he asked McGee. "Sometimes Sam forgets to use the public address when we work with other agencies, and he sends information to my secured email."

"Your Assistant Director sent something over just a few minutes ago," McGee replied. "I forwarded what we had to him, and he said he'd have his team take a second look. They found a few more Tax ID numbers for businesses under Salazar's umbrella, but there hasn't been recent activity from any of them."

Mac typed the passwords necessary to access the secured part of his laptop's programs, and brought up his email. Sorting through the normal 'bureaucratic nonsense' generated by the paperwork pushers at the Foundation, he filed them in the 'I'll get to it' folder of his inbox. That left a few messages from an old friend of his, an actress named Penny Parker, who was the celebrity face on a few human-rights issues the Foundation was helping out with. The last message was from Sam, and the subject line read, "Ceiling Tiles." Mac frowned, recognizing their own personal code and translating it to mean 'Heads-Up!' Making sure there wasn't anyone reading over his shoulder, Mac opened the email.

"Please inform Agent DiNozzo that Salazar has no ties to the Middle East, governmental organizations sourced in the Middle East, agents present or past of governmental organizations sourced in the Middle East, or families with surnames of Biblical origin," the short message informed him.

MacGyver's Voiceover: Oh, boy… Thanks for the warning, Sam. I'm too tired to deal with this right now, but I'm glad I knew about DiNozzo's prying in advance. I can't say I'm surprised he's been asking about her. He's a lot more subtle about it than I expected. *sigh*… I wish I could answer his questions. Time to brush up on the poker face…

Gibbs' phone rang at that moment, and he lifted the receiver. "Abs? You okay?… Yeah, hang on!" Gibbs looked over at MacGyver. "Abby just got another idea, and she wants you to come back down to help her."

Mac squeezed his eyes closed as he apparently waged an inner struggle. "I'm cooked," he finally admitted. "I just don't have anything else to give right now." He tugged off the tattered lab coat, folded it, and held it out for McGee. "Tim, if you still have any energy, I'm calling you as my pinch-hitter."

McGee looked to Gibbs for permission, and when the nod was received, he picked up the lab coat on his way to the elevator. "When was the last time Abby had a Caff-Pow?" McGee asked, pausing as that thought hit him.

"Those Bisphenol-A laden containers of caffeinated food coloring?" Mac queried with a shudder. "I think she finished her last one an hour ago."

"Uh-oh… She's running low!" McGee said in concern as he picked up his pace.

"I'm on it," Gibbs sighed heavily as he pushed himself to his feet. Sparing Mac a glance, he explained, "I'd better check on her too… should make sure she's not melting anything structural down there."

"I'm sorry in advance," Mac called helpfully at his retreating back. Gibbs threw a challenging glance over his shoulder and disappeared behind the silver doors. Muted chuckles echoed from the few remaining agents scattered around the room. 'He hasn't changed much," Mac confided with a grin.

DiNozzo nodded in an echo of Mac's amusement. "Yeah, he's been like that as long as I've known him."

Mac's eye-roll was expressive. "I hate to break it to you, but he has mellowed, just a bit."

Tony grew thoughtful. "Yeah, I can see that, actually." Lost in reverie, Tony's gaze darkened as he stared at Gibbs' empty chair.

"Hey, I've got a question for you," Mac said, leaning back and crossing his arms. "How long has Gibbs known Abby? He's got a real 'Papa Bear' affection for her, doesn't he?"

"He's known her longer than I've been here," Tony agreed. "She is and always will be his favorite."

"He looked really worried about her when our experiment decided to blow up on us," Mac agreed. "You know, when we were out in the woods and Ellie got hurt, Gibbs had a similar look on his face." He paused as he noticed that Tony did not look surprised. "I know Gibbs has a protective streak a mile wide, but what's with this paternal concern?"

Tony seemed lost in memories. "There have been three long-term agents sitting at that desk since I started with NCIS. We lost two of them. We really don't want to lose the third."

"Lost… oh, that doesn't sound good," Mac said with sympathy.

Tony nodded. "Our first was Kate. She was Secret Service before she joined us."

MacGyver's Voiceover: My grandfather told me once that if you're looking to catch a specific fish, you need to use the right bait. If the fish won't bite, don't be afraid to change what's on the end of your line. Tony's got a bunch of hooks in the water right now, and he's doing all he can to distract me from them. If I'm not careful, I'll get snagged but good!

Forcing his tired mind to stay sharp, Mac kept going with the conversation until he could figure out where Tony was headed. "She sounded like a capable agent… And let me guess; Gibbs pulled his 'Papa Bear' routine on her a few times, too."

"Yeah, that protective streak kicked in quite a bit," Tony agreed. "Kate brought that out in all of us. She was killed…"

Mac winced with him. It was never easy to lose a colleague. "I'm sorry." Mac knew it had been over ten years, but the pain in Tony's eyes was still fresh.

"A terrorist was hunting Gibbs, and he killed Kate to hurt Gibbs… I have to say, it worked…"

"It happened right in front of you both, didn't it?" Mac commiserated.

Tony swallowed hard, and Mac could tell he was reliving that horrible day. "We were talking to her. She was getting on to me about something, and suddenly she was… laying at my feet, dead. Gibbs couldn't find the sniper right away… He wasn't himself during the investigation."

Mac had enough of his own nightmares to deepen the sympathy in his voice. "You did find the sniper, though," he hedged. Feeling Tony's penetrating gaze on him, he focused on keeping his both his breathing and the expression of sympathetic curiosity on his face from changing.

"Yeah, we found him. He was taken out, in Gibbs' basement."

Voiceover: Oh… well done; you walked right into that one! She told you all about that day. Mac, how could you not see that coming?

Tony shrugged. "Then we got Ziva." Although nothing in the younger man's face changed, it was obvious Tony didn't get the reaction he wanted. In a conversational tone, still tinged with sadness but growing warmer, he kept talking. "Ziva David was Mossad. She joined the team as a Liaison Officer shortly after, then became a full-fledged NCIS agent."

"That must have been interesting," Mac allowed, struggling to keep his tone even as his mind raced furiously. Deciding that he couldn't play completely ignorant to the woman's existence, he added, "She was with you for seven or eight years, right?"

Tony pounced, eagerness slipping through his carefully crafted facade. "How did you know that?"

Mac forced a smile. "How comfortable would you be, working with someone who knew everything about you while you knew nothing about them?" Trying not to smirk at the sudden confusion that leapt into Tony's startled eyes, Mac continued, "Turn about's fair play, DiNozzo. I know you looked up my file. I looked up all of yours."

Tony processed that for a few long moments, giving Mac a chance to prepare for what might be coming next. It was clear that Tony didn't know whether to believe that entirely or not; Mac could sense his desperation for any information on their mutual acquaintance, but Mac also knew how dangerous sharing that information would be.

"If you found out we'd gotten into your file, I'll have to talk to McGee about covering his tracks better," DiNozzo said with brittle humor.

Voiceover: Uh, wait a minute… you'd printed my Ops packets out and put them on a bookshelf! Don't yell at McGee for that breach!

Tony continued speaking. "But since you brought it up, I'm curious… What got you into this line of work?"

Mac covered his surprise at the change in DiNozzo's tactics. He drew the moment out with a reminiscent sigh. "I think I was born without the ability to keep my nose out of things. It also seems I have a chronic perverseness to saying, 'No'. Especially to my friends. That's why I'm sitting here today, in fact." Meeting DiNozzo's eyes, he recognized genuine interest in the new topic of conversation, and determined to keep it there.

"What's the most dangerous thing you've ever done?" Tony asked, leaning forward and propping his elbows on his desk.

Voiceover: Allowed myself to be left alone with a skilled interrogator hungry for information I can't give him?

Mac blew out a puff of air as his eyebrows climbed upwards. He was thoughtful for several long moments. "Oh, jeez, I dunno…"

"This case must be bringing up a lot of memories for you…"

Voiceover: You have no idea, kid! God, eighteen years lost! I still can't forgive myself for that, even though he has…

"…You've dealt with all kinds of crazy situations; rescuing people behind enemy lines, preventing massacres, dealing with explosives all over the world with the DSX. You know, it's a good thing you're on our side; some of those IED's you built yourself were kinda 'out there'."

Feeling the figurative rumble of an impending explosion buried in this conversation, Mac turned his lips down in displeasure. "Yeah, I've nearly blown myself up more times than I care to contemplate… Today is another sterling example of that!" He gazed for a moment at his hands, rubbing his printless fingertips together.

"Did you learn about explosives in Vietnam? Or did your chemistry background point you in that direction?"

Mac knew his expression didn't change because Tony wasn't shrinking away in worry. For that, he was grateful. Voiceover: Yeah, she told me he was good. He's pushing buttons I forgot I had. Talking about memories…? Deep breath, now. You don't ever have to go there again; that part of your life is over and done with, never to be repeated. Change the subject. Away from the one he's trying to get at, while we're at it. He can't know… She doesn't want him to know. I don't agree with it, but I have to respect her wishes. I just hope he finds out…before I did. And not the way I did, either… Okay, okay, get yourself together now. C'mon, MacGyver, get it together.

Forcing a smile he was nowhere near feeling, Mac attempted a cavalier wave. "Knowing as much as I do about chemistry and physics has been both a blessing and a curse. It's gotten me into a lot of trouble, but out of it enough times that I'm still kicking around."

Tony's sudden grin threw Mac off. "It can't be all bad; you've helped a lot of people. That's gotta mean something!"

"Oh, it does, for sure!" Mac insisted. "I usually end up helping the people that are really in trouble, and getting them out of it requires more… inventive measures, shall we say?"

The conspiratorial grin on the younger man's face sent prickles of concern crawling up Mac's spine. "Leaving the boring 'easy saves' for the others…so you get all the fun!"

Mac actually laughed. "That's one way of looking at it, I guess!" He sobered as he looked at the information that was still displayed on the plasma screens. "I just wish this was a little easier of a save. I really want to find the guy that shot Andy. I didn't know the kid personally, but my friend adopted him, so that makes him pretty close to family in my book. Andy's got a long recovery ahead of him, but it might make it just a bit easier knowing the guy who shot him is behind bars."

"We'll get him," Tony assured him. "We always find what we're looking for…"

The extra meaning that flashed briefly in Tony's eyes changed to friendly curiosity as Gibbs' return changed the atmosphere in the bullpen. "Abby is properly caffeinated, so all is right with the universe?" Tony confirmed.

Gibbs settled back into his chair. "They're both still alive down there," he shrugged. "She wasn't really happy that you benched yourself, though," he informed MacGyver.

Mac scrubbed a hand over his tired eyes. "If I'm going to be of any use to anyone tomorrow, I'd best get some real sleep tonight. Since you're my ride back, are you ready to go?"

Gibbs debated for a few moments, then nodded. "DiNozzo, you go home too."

"Good night, Tony," Mac offered as he gathered his stuff.

Tony returned a friendly nod and a loaded smile. "Pleasant dreams."

Voiceover: Not likely…