It was a hot summer night. The type of night where the air was thick and still and the last place Caroline wanted to be was out in it, but duty had called. She'd been asleep in her king size bed, dreaming of something a lot nicer than a muggy August night, when the phone had awoken her. Aaron Hotchner and the Behavioral Analysis Unit of the FBI needed her and she could never say no to that man. So, she walked down the hallowed halls of Quantico, her black pumps causing her footsteps to echo as she made her way down the hallway to the familiar conference room. "So, you boys have confused your pistols with your privates again?"

"Isn't that the only reason anyone calls you?" Agent Hotchner smiled as he whipped around to see his old friend. "Caroline, how are you?" He shook her hand, noting just how well dressed she was for three o'clock in the morning in her signature black pantsuit.

"So, what are we dealing with here?"

"An L.D.S.K. I need to know what kind of weapon we're up against because we have no projectile."

"OK, give me what you've got." Sitting down, she grabbed the file but quickly stood up again. "You have the shot on video tape?"

"Yeah, a news crew was in the area when the shot went off."

"I want to hear it." Hotchner cued up the tape on the monitor and played it while she closed her eyes, but she quickly frowned. "Again." This time she was sure of what she heard and signaled him to shut it off. "You're right. It's not your typical projectile. Your weapon is a rifle, probably a Remington 22 caliber single shot bolt action from the sounds of it, but the sound of the bullet leaving the chamber sounded foreign. If I had to guess, I would say that it was some form of homemade ammo, maybe ice, though I've only heard of that once before."

"You got all that from listening to the shot twice?" The tall lanky younger man questioned.

Caroline smiled. "Dr. Reid, that's why they pay me the big bucks."

"How would someone go about making a bullet out of ice?"

"Liquid Nitrogen and a bullet mold. Packed correctly and with the right amount of powder, it can reach its intended target before dissipating completely, becoming almost untraceable. While not my preferred choice for a long range projectile, it is conceivable. You're looking for someone with an immense knowledge and passion for firearms. Probably military trained, but he's definitely been handling a weapon almost as long as he's been alive."

"So we're looking for a male version of you." The good-looking black man seated at the table finally stood up. "CJ, that doesn't give us much."

"Hey, I'm not the profiler, Derek. The only reason I'm called out of my office is because you guys can't figure out the difference between a rifle and a shotgun. I can tell you that he probably won't fire his weapon more than once at a scene. It's a single shot bolt action. He's got something to prove. One shot, one kill. He's not the type to over play his hand or take chances. He's also not going to leave you much in the way of evidence."

"And he will strike again." Hotch looked at the floor as he began pacing.

"I'd like to be there when he does. I can tell you more if I see his handy work."

Hotchner looked to the older man in the room and got a nod. "Sure, but you have to be packed and ready to go in a half hour."

"My bag's outside."

Hotchner was happy to have her along for this case. A knowledge of firearms like Caroline's was a gift and he was counting on that gift catching this lunatic running around Pittsburgh with a rifle.

"Have you ever worked in the field, Agent James?" Derek joked as he sat next to her on the plane.

"Once or twice, Agent Morgan. Including once where I saved your sorry ass." Caroline quipped back with a smile.

"Ouch, CJ." He laughed.

"No, you had a job to do and so did I. No regrets.'

"Never." The smile faded and he sat back in the seat.

"So, how's Dr. Reid working out? I know about the trouble he was having with his firearms quals."

"He's getting better. I think Hotch is working with him, but if you want to broach the subject, I don't think he'd turn you down." He laughed again. "I don't think any man would turn you down. He'd be too afraid you were going to take him out." Taking her hand, he squeezed it as she laughed a light and easy laugh.

"They dated once." The older agent sat down across from Dr. Reid when he saw him studying the interaction of Caroline and Morgan.

"They just seem very comfortable together." Reid thought for a minute. "Gideon, how does Hotch know her?"

"They've worked together before. She's the bureau's best ballistics technician and sniper."

"I'm just amazed that she's able to identify a gun by the sound."

Gideon smiled. "She's been handling a firearm since she was a child. Her father was a Marine sniper, as she was, and she was a music major at Annapolis. It's a gift that the FBI is very lucky to have access to."

"And I feel privileged to have access to the FBI's firepower." Caroline smiled as she sat down next to the young agent, shooting Gideon a look that caused him to nod and relocate his seat. "Dr. Reid, do you mind if I ask you a question?"

"I think you just did, but ask away." He watched her smile and couldn't help but smile in return.

"I see working with these clowns has rubbed off." She rolled her eyes. "OK, well, here's my question, and feel free to stop me if I get too personal. I heard about your troubles at the range so my question is whether or not you would want to work with me while you're in town. We can get you past those difficulties."

He thought for a minute and then nodded. "That might work." They shared a smile and she lightly squeezed his hand.

The next day, that smile was gone as she studied the new crime scene. Their Long Distance Serial Killer was good. Definitely military trained and this time he changed his weapon and ammo. He was showing off because he'd killed four people and thought he was going to get away with it. The profilers were working on why he did what he did and left her to focus on why he would suddenly change his weapon. It puzzled her. Most times, snipers found a gun they liked, that they had success with, and they stuck with it. The only time they would change would be if conditions changed and conditions hadn't changed. It was still a runner, marathoner in training, it was still a public area, and the subject was still killed with one shot.

"CJ?" Morgan stuck his head into the conference room three hours after they'd arrived and found Caroline staring at pictures of all five victims.

"I don't get it, Derek." She gestured to the first three photos. "These, he's showing off. This fourth one, he's sending us a message that he is at the top of his craft, but this fifth one, this fifth one is different. It still took skill, but it doesn't have the same flair and it's a different gun, a different caliber." She pulled down the first photo and the last. "It's a different guy."

"Show me." He sat down as she explained the difference in the wounds, the weapons, and the ammo.

"I'd say if you come out and credit this kill to him, he'll show us what he's made of, and I bet he'll slip up."

"You're betting another person's life on that, Caroline." Hotchner walked in. "I want him before a sixth body shows up."

"Aaron, this is the only way. This fifth kill had no style. It was a straight shot in the stomach. I could do that blindfolded. It wasn't as skillful as the first four. Either your guy is getting tired or this fifth one is a different shooter."

He nodded. "OK, tell J.J. what to tell the press and we'll wait."

Sure enough, once the FBI came out and told the media that the 'Runner Gunman' had struck again, it wasn't more than an hour before they got called to another crime scene and this time, Caroline was sure that it was the unsub they were looking for. Looking around, she spotted the perfect spot for a sniper's nest and they found an empty cooler. That was how he was transporting his frozen ammo and there were fingerprints on the handle.