Rating: PG-13

Warning: Graphic Violence, Depictions of War, Heavy Use of Original Characters

Notes: This story is pretty light on Hawaii 5-0 characters but that is due to the fact that I'm using this story to provide background info for the stories that will come after it. Future stories will focus heavily on the 5-0 team. FYI: the series will eventually be slash though there really isn't any in this part.

Disclaimer: I do not own Hawaii 5-0 or any of its characters, though most of the characters in this particular story are mine.

Air Force 1st Lieutenant Anthony "Tony" Liu had only been out of medical school for two weeks when he was deployed the first time. He was at school in New York one day and in a war zone in Afghanistan the next. It was jarring to say the least.

Tony was good at his new job though. His unit said he had nerves of steel. Tony was part of an emergency medical unit sent into hostile areas, usually by helicopter, to rescue injured soldiers. When they arrived at their destination, they did triage and evacuation of injured soldiers. Tony loved it. He loved the excitement of being on the front line and the satisfaction of protecting the people who were protecting everyone else.

One day, things went very wrong.

"Bad news, guys. We're hit and we're not gonna make it to neutral ground." The co-pilot's voice was tight with suppressed anxiety as he spoke to Tony's unit while the pilot called in their status and coordinates. "Brace for impact." The helicopter jolted and shook violently on it's way down.

The next thing Tony knew, someone was shaking his arm. His body ached and his head pounded. He could hear gunfire nearby.

"Let's go, Doc. Wake up!" When Tony opened his eyes, Lance Corporal Eddie Willard still had a hand on his arm. The other man was grim faced but calm.

Tony struggled out of his seat and glanced around the wrecked helicopter. The pilot and co-pilot were clearly dead, as were two other members of his unit. He and Willard were the only two from his unit who had survived. His patient was alive though. Private Tanya Collins had a broken leg and a few superficial lacerations as a result of an IED explosion. Tony had splinted the leg on site and covered the worst of her cuts while they were in route. Now he grabbed her under the arms and pulled her to her feet. He threw an arm around her waist and pulled her arm across his shoulders, trying to take some of her weight off her bad leg. Willard was at the bent door, staring out at the small town they'd come down in the center of. "Come on. We've got to get out of here." They could hear shots bouncing of the far side of the helicopter. It was only a matter of time before their attackers moved closer.

Tony and Collins joined Willard at the door.

Willard nodded at them and said, "Doc, you two make a run for those buildings." He pointed to a nearby cluster of houses. "I'll cover you. When you get there, give me a 30 second count and then cover me while I catch up."

Tony nodded and tightened his grip on Collins. On Willard's mark, he ran, dragging Collins with him. When he reached the buildings, he propped Collins against the wall beside him, counted to 30 and leaned around the edge of the building to cover Willard. As soon as the other man had joined them, the three took off between the buildings at a run, keeping to cover as much as they could.

They moved constantly until dark, when they took shelter in a small empty shed on the edge of town. Collins passed out almost as soon as Tony settled her on the ground. She'd continued through the pain from her broken leg as long as she was able. He exchanged a glance with Willard.

"Do you have a radio?" Willard asked.

Tony shook his head. "I lost it during the crash."

Willard sighed. "Mine's dead." He glanced over at Collins. "And she doesn't have any of her gear."

"Any ideas?" Tony dropped down beside Collins, checking her vitals while he had the chance.

"I'm thinking we better head out of town asap. By morning, our friends with the guns back there will probably be going door to door looking for us."

Tony nodded. "Probably." He sat the rest of the way down to take advantage of the little rest time they could afford.

Willard dropped down across from him. "We'll rest for a few minutes, then we'll head out."

Thirty minutes later, the two men helped a groggy Private Collins to her feet and headed out into the night.

They walked in silence for a while, keeping close to the edges of the buildings until they reached the edge of town. Willard studied the area ahead of them with a frown. "There's no cover for miles."

Tony sighed and tightened his grip on Collins. She was supporting more of her weight now that she was a bit more awake and Willard had been able to return to his position taking point. "There's really no help for it. We can't stay in the village and if we don't go now, it'll start to get light out before we're very far away. We'll be spotted immediately."

"I know. I just don't like it." Willard led the way along the edge of a road leading out of town in the general direction of where they had decided they were most likely to run into American or NATO forces.

They had been walking along the road for about three hours when Willard suddenly froze. Tony and Collins stopped a few feet behind him.

"What is it?" Tony called quietly.

Willard took a deep breath and craned his head to look back at Tony and Collins. "I-I think I stepped on a mine."

Tony felt as though the bottom had just dropped out of his stomach. Collins shook her head.

"Ok," Tony said. "I'm gonna help Collins move away a bit, just in case, and then I'm gonna come right back and we'll figure out how to get you out of there." Tony was already pulling Collins off the road.

"So you're a doctor and an explosives expert, Liu?" Willard's tone was calm but Tony could hear the underlying fear.

He helped Collins sit against the back of a large boulder about 30 feet away. "I wouldn't say I'm an expert exactly but I'm a smart guy. I follow directions well," Tony called.

Willard smiled. "I know you are, doc. That's why you and Collins are gonna get home." He stepped off the mine.

The explosion knocked Tony off his feet and he lay on the ground for a long moment before sitting up to look at the small crater where Willard had just been standing.

Collins had already scooted around the edge of the boulder to his side. "What just happened?"

Tony's face scrunched with the force of his emotions. "He did it on purpose. He didn't think I could help him." Tony scrubbed a hand over his face and through his hair, sending dust floating around his head.

Collins closed her eyes for a moment and then leaned further out to peer around the edge of the boulder at the place where Willard had been standing. She and Tony could see debris from the explosion that had clearly been part of Willard's body. She gulped and leaned back against the boulder, trying to slow her breathing.

Tony stared at what was left of Willard's body for a moment before climbing to his feet and moving toward him. Most of Willard's body was in one piece. His head and arms were still attached to his torso, though his left leg had been blown off and the other just seemed to be gone. Tony ignored his rising nausea as he bent down beside the other man. He checked his pulse, though he knew Willard was dead, and detached one of his dog tags. He stood, slipped the tag in his pocket and turned away.

Collins was on her feet when he reached her, leaning heavily on the boulder. "We better go. Someone could have heard that."

Tony nodded and reached an arm around her. "We'll stay further off the road."

Collins nodded and the two walked on.

He was aware that he shouldn't be able to see the barely detectable shape of a buried mine or hear the virtually silent movement of animals as he hunted for their meager meals. Tony tried not to think about it too much. After all, it kept saving their lives.

Collins and Tony were on their own in hostile territory for five weeks before they startled a friendly convoy by appearing in the road in front of them. They were returned to base for medical treatment. Tony reported suffering from migraines throughout the time they spent evading capture, though he did not attempt to explain the impossible things he'd suddenly been able to do. Collins reported a broken leg that was well on its way toward being healed and that her companion had suffered from brief periods of near catatonia, as well as seeming to have the ability to hear and see things beyond the scope of average human senses.

Two days after Tony and Collins were found…

Colonel James Ingles found Tony in the mess tent. Tony started to come to attention as soon as he spotted the Colonel but Ingles waved him back to his seat. He sat down across the table from Tony.

"Good afternoon, sir." Tony's face was wary. He'd been questioned a lot over the last couple days regarding his reportedly enhanced senses and he still wasn't sure how to answer their inquiries.

Ingles nodded in response to the greeting. "How are you doing, Lieutenant?"

"Good, sir. I'm really glad to be back."

"I bet." Ingles watched Tony push his food around his plate. "Don't like your lunch?"

Tony dropped the fork and shrugged. "I don't have too much of an appetite today."

Ingles noted the spicy chicken on the other man's plate. "Is it too spicy now?"

Tony paused, uncertain how to answer. Somehow, that seemed like a trick question.

Ingles nodded as though he had already answered. "I'm going to guess that the answer to that is yes." He leaned his elbows on the table in front of him and lowered his voice before bringing up the expected topic. "I spoke with Private Collins a little bit ago. She's doing quite well, told me that you were a hero. She also told me that you evaded capture because you could hear and see more than the average. She was pretty awed, in fact."

"I don't know what to say, sir. I can't explain it."

"That's okay, Lieutenant. I'm going to tell you what I think is going on and you tell me if I get anything wrong."

Tony nodded. "Yes, sir."

"Good. All of your senses are heightened. Collins mentioned you could hear and see much farther than she could. You can't eat the foods you used to, such as the spicy chicken you've got there, because the taste is too strong. I've also noticed you've got a bit of a rash on your neck where your shirt has been rubbing all day. I'd say that means your sense of touch is heightened as well. Is your sense of smell stronger too?"

"Yes, sir." Tony paused. "I don't understand how this is happening."

"I think I do. I've heard of something like this before. When certain people are placed in a dangerous situation where the survival of others is at stake, these heightened senses seem to show up. Obviously, this doesn't happen to everyone. But for a select few, these abilities come online just when they're needed most. The social scientists call these people sentinels"

"And you think that's what's happened to me? You think I'm a sentinel?" Tony asked.

"Yes."

"And there are others? I've never heard of sentinels."

Ingles nodded. "Yes. Most are employed in careers where they protect people, like military, cops, or firefighters. Careers where they're more likely to be put in dangerous situations that would trigger their senses. Careers where they can use their senses to help others. You haven't heard of them because, for the most part, they generally try to keep a low profile. I would imagine that they worry about being exploited."

Tony shook his head. "I'm sorry, sir, but that sounds impossible."

"I know it does but you have to admit that the things you've been able to do lately are a bit impossible."

Tony slumped and ran a hand through his hair. "I suppose they are."

"It's not a bad thing, Lieutenant. Sentinels make fantastic soldiers." He pulled an envelope from his pocket and pushed it across the table to Tony. "Your new orders."

Tony opened the envelope and noted that he would be moving to another base in Afghanistan in less than two days. "What does this mean, sir?"

"Your new abilities mean you'll be getting a new assignment, new training. I don't know any of the details."

Tony nodded and stuffed the paper back into the envelope. He wasn't sure what else to do.

"There's one more thing about sentinels that you should know." Ingles leaned back but kept his voice at the same low volume he'd been using. "Sentinels usually come with guides. In this context, a guide is someone who anchors the sentinel. They provide someone for the sentinel to focus their senses on so that they can utilize their abilities to full capacity. The sensory spikes you've been having are pretty common to a sentinel without a guide, as are episodes where a sentinel focuses in too far on one sense and loses track of their surroundings. If you find a guide, their presence will help with that, though you'll learn to control a lot of it on your own."

"How do you find a guide?" The word resonated within Tony somehow. He felt in inexplicable and terrifying yearning.

Ingles shrugged. "I really have no idea. From what I've heard, you'll know them when you meet them. If you do find your guide, let your superior know right away. They'll want to make sure you're always deployed together. Hopefully, your new superior officer will be able to tell you more." He studied Tony for a long moment. "You okay?"

Tony nodded. "It's a lot to take in, sir."

Ingles smiled. "And you don't entirely believe me. That's all right. I just wanted to make sure you had all of the information I could give you." He stood up.

Tony followed suit and said, "Thank you, sir."

Ingles nodded and left the mess tent.

Tony sat down again and stared at his inedible spicy chicken for a long time while he attempted to process everything that had happened over the last few weeks and the explanation he'd just been given. It was impossible but it would actually explain a lot.

Two days later, Tony reported for duty at his new assignment. His immediate superior was Marine Corp Major Alex Powell.

Tony zoned out twice the next day during training exercises that were specifically designed with sentinels in mind. Major Powell easily pulled him out of both. Tony was a smart man. It didn't take him long to figure out that Alex was his guide.

Two years later…

"So that's my story. It does sound a lot like what you described your friend experienced." Tony sat on his living room couch, feet on the coffee table in front of him and cell phone pressed to his ear.

"I thought so. I told him a sanitized version of what I saw you guys do on that mission in Peru but he still doesn't believe me. It's been two weeks since that whole thing happened and he claims not to have had any more symptoms." Steve's voice came across frustrated and just a little bit whiny.

Tony grinned. "I've heard it can happen that way. The senses come and then they go. They'll be back though. Now that he's online, it's just a matter of time."

"I wondered. I'm worried they'll come back at a bad time, like right in the middle of a firefight."

"That's certainly possible. That sort of situation could definitely trigger his senses again."

Steve was silent for a moment as he contemplated the likelihood of 5-0 being involved in a firefight in the near future. The chances were not in their favor. "I do have one more question for you."

"What's that?"

"Is Alex your guide?"

Tony smiled. "Yeah."

"That helps?"

"Oh, yeah. The first couple days of training after I came online were really hard and whenever Alex was nearby, it was just like a switch had been flipped. I could use my senses more and for longer without the nasty side effects when he was with me. His presence helped almost right away and it only improved over time."

Tony could practically hear Steve's contemplative expression. "So we need to find a guide for Danny. That's the best way to keep him safe."

"It is but I don't think you really need to worry about finding a guide for Danny. When he meets his guide, he'll know. It's not really the sort of thing you can order online."

"Presuming that he eventually admits that he actually has enhanced senses."

"Presuming that, yeah."

"Any idea how we could prove it to him?"

Tony grinned. "You know, I think I just might. I'll call you back in a bit and let you know."

"Um, okay." Steve's voice was confused.

Tony hung up the phone and went looking for his guide. A vacation in Hawaii sounded like a pretty great idea.

THE END

NOTES: I know this story was super heavy on original characters but I promise I'm already working on the next story in this series. The next one will focus on Danny, Steve, and the rest of 5-0, though the OCs introduced here will play a part.