I do not own Castle or NCIS LA. No copyright infringement is intended and no profit is being made off of this.

Thanks to veggiewoppa for reading it over for me.

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"Would you look at all those people?" Richard Castle surveyed the crowd gathered outside the bookstore with a grin. "And they're all eagerly waiting to get to me."

"Mr. Castle, please move back," the manager instructed, wringing his hands. "The last thing we need is for them to go crazy seeing you through that window. We want things as calmly and orderly as possible."

Castle gave the nervous man his best smile. "Don't worry; I've done this lots of times. It'll all go smoothly, I'm sure."

"Whatever you say." The man didn't sound convinced. "But please, Mr. Castle, come sit down. Those doors will open before you know it." He was fidgeting with the edge of his jacket, darting nervous glances out of the doors. "This is such a fire hazard," he mumbled to himself.

With a good-natured shake of his head, Castle walked over to the folding table that had been set up for the event, piled with copies of his newest novel, as well as his older works. A large cardboard poster of the writer himself was propped next to the table, with text proclaiming that Richard Castle would be at the store in person to sign books and greet fans as soon as the place opened that Saturday.

He took a seat in the metal folding chair and straightened the row of black Sharpies in readiness for the crowd that would soon rush through the doors in anticipation of meeting him.

Several hours later, Castle had already signed dozens of copies of almost every one of his books, and the people still kept coming. The line had been out the door since the store opened, and it didn't look like it would be letting up anytime soon. The store had done its advertising well, and Castle knew he would be busy until the allotted time for his signing was up. He grinned. There was nothing like being the object of so many adoring fans' attention.

He was just returning a now-autographed copy of Heat Wave to a slightly-overweight, middle-aged woman when the next fan in line stepped up to the table. He was average height, with shaggy, light brown hair and a no-worries attitude about him that held something a little more determined as well. And when Castle studied the man more carefully, he was nearly positive he could see a small bulge under the man's shirt.

Not completely sure what the laws were on concealed carrying in California, Castle settled for flashing his best smile. "Thanks for coming. How should I make this out?" he inquired, accepting the obviously brand-new book the man handed him.

"Uh, Marty's fine," the man replied. Castle could tell he was distracted, although he was trying to appear as interested as possible in the books and their writer.

"Naked Heat!" Castle observed. "Good choice! So you've read Heat Wave already?" he asked, opening the book to the title page and putting his marker to the paper.

Marty nodded. "It was... really good," he answered, a bit evasively, Castle thought. "I haven't really gotten around to getting this one, but I figured getting it signed by you was the perfect opportunity." A funny look crossed his face a moment later.

"Everything all right?" Castle inquired, not having heard Kensi's remark through the team's earpieces.

"Yeah, yeah, great," Marty assured him, though Castle wasn't convinced that things were quite as fine as the man wanted him to think.

"Well, thank you for coming," Castle told him, returning the novel. As he did so, a woman passing by the book table caught his attention.

She was tall and slim, with dark hair tied back in a ponytail and dark eyes that searched the crowd around her. Her leather jacket and jeans complimented her figure nicely, he couldn't help noticing, but the part that really caught his attention was the way she was watching the crowd. She had all the movements of a cop, and Castle could tell from experience that she was obviously looking for someone. His curiosity was piqued. Either she was security that the bookstore hadn't told him about or there was something else going on.

He turned back to say something to Marty, but the man had already moved off. Castle's brow furrowed; there was obviously something going on. Or at least, he was curious enough that there had to be. Beckett would probably tell him not to worry about it, but he was fairly certain there was at least something going on.

And although he still had books to sign and fans to greet, half of his attention was now occupied with figuring out what that something was.

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Special agent G. Callen scanned the crowd as he moved among the throng of people, trying to spot their target. "Anyone see anything?" he asked in a low voice.

"Nope," Sam Hanna's voice came through Callen's earpiece, echoing Kensi Blye's, "Nothing yet."

"Same here," Deeks put in. "Hey, do you think Hetty will reimburse me for this book I bought?"

"Eric," Callen ignored the detective in favor of addressing the tech who had remained at the operations center. "Any sign of Mason?"

"Not yet," Eric Beale replied. "I've connected to the store's security system and am currently running facial recognition, but there's no sign of him yet."

"Remember, the most likely place for Mason to set something off would be at one of the support pillars or the near the entrance," Nell Jones spoke up next. The sound of typing came through in the background as she continued, "A device placed in one of those locations would cause the maximum amount of damage and chaos."

"Crazy mad bomber out for revenge on the country," Deeks commented. "Creating insecurity and confusion one explosion at a time."

"Can you stop talking, just for a moment, or will the world implode if you do?" Sam asked good-naturedly.

Callen interrupted the conversation before Deeks could get a comeback out. "I've got him. South entrance, near the doors."

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"And thank you," Castle gave yet another fan yet another smile as he returned the stack of three books the girl had handed him. The young woman and her friend, both of whom the writer guessed were at least a year younger than his own daughter, giggled as they scurried off. He was just starting to greet the next person in line when there was a sudden commotion near one of the store's side entrances.

Castle, as well as most of the patrons in line and throughout the store, paused their current activities in an attempt to make out what was going on near the doors. Then several screams cut through the air, as well as a man's shout. Castle made out the words "Federal agent!" before the people nearest the noise began pushing against each other in an attempt to get as far away as possible.

His interest piqued, Castle stood from his seat to try to get a better view of the situation. As he stepped out from behind the table, the crowd in front of him parted quickly and two men came rushing in his direction.

The first man was carrying a backpack and running as frantically as any criminal Castle had ever helped Beckett chase down. His pursuer, who had a badge clipped to his belt, had his weapon out in front of him.

"Mason!" the agent yelled again. "Stop right there!"

However, Castle observed as he took in the scene, the man seemed to have no intentions of obeying the order.

The thought that the pair was barreling straight towards him suddenly crossed the writer's mind, as well as the thought that he could possibly assist the agent and help bring whatever was going on to an end. He grabbed one of the thick hardcovers on the table beside him and stepped to the side as he swung it like a baseball bat. The fugitive was running past him just then, and the book connected with his face with a solid thunk.

Mason dropped to the floor, dazed, as the agent pulled to a stop beside Castle.

"Good aim," the agent complimented as he bent to clear the man on the floor of any weapons.

"I think you broke my nose, man!" Mason exclaimed. He had his hand cupped over his face, and Castle could see a bit of blood leaking through Mason's fingers.

"That's the least you deserve for what you were trying to do." The agent had moved the backpack to the side and now hauled the moaning man to his feet. He nodded to Castle. "G. Callen."

"Richard Castle," Castle returned. "So you're really a federal agent?" he asked, unable to keep the excitement out of his voice.

"Yes," Callen replied.

Castle was about to ask him to go into more detail, but was interrupted as another man joined their group.

He wouldn't like to go up against this newcomer in a fight, Castle noted to himself. The larger man was well-built and there was something about him that scared away any thought of crossing him.

"I saw what you did there," the man told Castle. He paused, and Castle resisted the urge to squirm at the look the agent directed his way. "Good job," Sam finally added, extending a hand. "Sam Hanna."

Swallowing, Castle managed a grin. "Well, thank you. I do have a little experience helping apprehend criminals with all the work I do with the NYPD, so I figured I'd give you a hand."

Sam just grunted; Castle couldn't tell if he was impressed or not. His writer's personality got the better of him, however, and he ventured to ask the question that was nagging at him. "Should I assume this is a top secret situation where if I tell the story you'll have to kill me, or can I ask for more details to use in a future book?"

"Speaking of books," Sam said, ignoring the question and gesturing at the one Castle was still holding, "I don't think you're going to be able to sell that one."

Castle glanced down at the hardcover, his face visibly falling as he took in the blood that was now smeared on the cover and the top edges of the pages.

"Don't worry; I'm pretty sure you can write that one off," Callen told him. "Just put it down to assisting the government of the United States." He shared a look with the other man; each with an amused look on their face that reminded Castle of Esposito and Ryan back in New York.

"Let's just say that you can only use as much as you hear in the news later," Callen told Castle as he and Sam marched their prisoner off towards one of the exits.

Castle watched them go, only slightly surprised when his fan from earlier, Marty, and the woman he had noticed in the crowd joined the agents. He started to cross his arms but stopped when he realized he still had the now-ruined book in his hands. With a sigh, he placed it under the table, though he couldn't help grinning as he took his seat again to continue the book signing.

He had quite the story to tell when he got back, although he wasn't quite sure the others back in New York would ever believe him.