North Star

a Castle / Avengers Crossover

in the "Four Winds" universe

by Laura Picken

Hi all! Well, writing a novel is a lot harder than I thought. So since I need an escape, I thought I'd bring you guys along with me. Hope you enjoy it!

DISCLAIMER: Like I own anything! This story is in the universe of my Castle Fantasy AU series "Four Winds", and overlaps with the series finale story, "Ascension". This story will make much more sense if you've at least read my story "Four Winds" (check my author page), although I'll try to write this so it's not necessary. And feel free to message me privately if you get lost. I'm happy to answer any and all questions. As for SPOILERS, I pick and choose plot points in Castle's season five to my liking, so if you haven't gotten to "Always" yet. Also, I know this may be out of sync with Avengers canon, but I'm placing the Chitauri attack in summer of 2013.

Let the adventure begin!

"See, Steve? Wasn't it worth getting out of that gym for this?"

Steve Rogers took a sip of his beer as he took in the scene in front of him. "It's a *party*, LT," he commented to his friend. "You dragged me all the way out of Brooklyn for a block party?"

LT chuckled in disbelief at his buddy's world-weary response. "You think I would drag you out for just *any* block party? C'mon, I got some guys you gotta meet."

"Sure," Steve replied with a shy smile, "just let me get a beer first."

"Al'right," LT agreed.

Steve made his way over to the buffet table as LT disappeared into the crowd. It was only when he turned around, though, that Steve realized something very important.

In the sea of people surrounding him, finding LT again was going to be next to impossible.

Steve twisted off the top to his beer and sipped the drink, grateful to give his hands something to do while his mind assessed the situation. LT was a police officer, a good man, and a good friend...who seemed to be making it his mission in life to help Steve *get* a life. In particular, LT seemed hell-bent on helping him make more friends than the three or four men who had some contact with him at the gym. The poor cop was probably dragging his friends through this mass of people, trying to follow through with whatever introductions he was so determined to make that night.

"Not much for big parties, huh?"

It took Steve a moment to realize that someone was talking to him. He turned to find the a young redhead was the one who had spoken. "Not really, ma'am," he replied politely. "Haven't really been to one in quite a long time..."

The redhead seemed hung up on the first part of what Steve had said to her. "Ma'am..." she commented with a quiet chuckle as she played with the label on her bottle of seltzer. "I think that's the first time anyone's ever called me ma'am..."

My God, she's so young...thought Steve. He held out his hand to the redhead in introduction. "Steve Rogers."

When their hands touched, the connection between them was electric. It surprised him to make that kind of connection with someone so young, but then when he looked into her eyes...She was a mass of contradictions. Her entire countenance gave off that air of youth and innocence that he heard in her voice when she first spoke. But her eyes...her eyes spoke of wisdom and intelligence far beyond her years and power beyond anything he'd ever seen. It was like he was shaking hands with the woman the expression 'Old Soul' was created for...

"Steve? Steve?"

It was only then that Steve realized that he hadn't let go of her hand...or found out who she was. He pulled his hand back like it had been set on fire, blushing as he realized that any attempt to look cool had long ago gone up in smoke. This caused the redhead to chuckle again...a low throaty sound that made him glad to have embarrassed himself, if only to have had the opportunity to hear it. "S-s-sorry...sorry about that," he stammered, his cheeks a furious red from blushing.

"It's okay," the redhead soothed. "I think it's cute."

Steve decided to throw caution to the wind. "Can we try that again?" he asked. "Now that I've gotten looking completely foolish out of the way, I'd at least like to know your name."

"Sure," the redhead agreed, eliciting another coveted chuckle.

Steve once again extended his hand to the young woman in greeting. "Steve Rogers. Nice to meet you."

"Nice to meet you, Steve," the redhead responded as she shook Steve's hand. "Alexis Castle."

"So what are you doing at a party hosted by the NYPD, Alexis Castle?" Steve asked with a smile. "Are you a police officer?" Alexis nearly spit out out her drink, a reaction that surprised Steve greatly. "Hey, are you okay?"

Alexis nodded. "I'm fine. Just...surprised, that's all. And no, I'm not a cop. I'm a sophomore at Columbia."

"A college student?" Steve asked, an eyebrow raised in surprise. "You're *really* far away from campus."

"My dad lives a few blocks away from here. He works here with the detectives at the precinct."

"Really?" asked Steve. "What does he do?"

Alexis took a sip of her drink to try and hide her smile. "He's a...consultant." It was only then that Alexis realized something about the progression of their conversation. "You don't know who my dad is, do you?"

Steve shook his head. "No, should I?"

"Richard Castle? The author? Wrote the Nikki Heat books?" Steve shook his head again, the name clearly not one that he recognized. "You don't get out much, do you?" asked Alexis.

Steve quickly became the one covering his tracks. "Not really, no..."

"Clearly." Alexis smiled. "So what do you do that keeps you from getting out so much, Mr. Rogers?"

Steve hesitated, trying to figure out a way to word his unique story without giving away any secrets. "I'm...retired. I used to be in the military."

Alexis' eyebrow lifted in curious surprise. "Really? I thought you had to be in the military for twenty years before you could retire."

Steve sipped his drink, his mind working furiously to try and backtrack on his statement. "I'm...older than I look."

"So who is this guy you want us to meet?" asked Ryan.

LT was practically bouncing on his heels with excitement as they headed back to where he thought Steve was going to be. "A friend of mine from the gym. He's...new in town."

"And why do you want *us* to meet him?" Esposito asked warily.

LT scratched the back of his neck, trying to explain his reasoning without giving anyone's secrets away. "Detectives...let's just say I think the three of you might have a lot in common."

When the three men reached the buffet table, they were all stunned by what they were seeing. Steve and Alexis had commandeered the end of one of the dining tables, and were striking up a conversation that seemed to be giving them the power to shut out the rest of the world. Esposito let out a low, protective growl as his instincts kicked in with a vengeance...the need to protect the girl he now thought of as his kid sister overriding almost all rational thought.

Ryan picked up on the change in his partner's emotional state immediately. Easy, Javi, he projected into the mind-link, they're just talking.

I don't know, countered Esposito, something about this guy feels...off.

Only one way to be sure, Ryan returned through the mind-link, let LT introduce you to him.

While he didn't recognize the young redhead that Steve was talking to, LT couldn't help but notice the hesitation in the men standing beside him. "Detectives, I swear...he's cool." He then turned his focus on getting his friend's attention. "Steve!"

Steve looked up from his conversation with Alexis to find his friend LT being flanked two strong-looking gentlemen. Apparently, these must be the men LT was so anxious for me to meet... "Hey LT," Steve greeted his friend, "how'd you figure out where I was?"

"Easy," LT teased, "When you want to find the wallflower you just look for the walls..." He stepped back to make the introductions. "Steve, I'd like you to meet Detectives Kevin Ryan and Javier Esposito. Detectives, this is my friend, Steve Rogers."

"Nice to meet you," Ryan said casually as he shook Steve's hand. LT then had to resist the urge to draw in a sharp, nervous breath as Steve shook Esposito's hand.

Esposito quickly had to resist the urge to gasp himself. Not from the shock of downloading the memories of the man in front of him, but from the memories themselves. Memories of an old war. Of lost love. Great physical deeds of heroism. And a red, white and blue suit of armor that seemed oddly familiar...

Ryan sensed the change in his partner's demeanor immediately. Javi? What did you see?

I'll show you later, replied Esposito. But I think I've heard of this guy before...

You've heard of him?

Yeah.

So who is he?

Esposito sent an image of a red, white and blue combat outfit down the mind-link to his partner. Bro, you ever hear of Captain America?

Ryan had to fight to keep the shock from showing on his face. No way...

LT had stalled for as long as he could, and Esposito knew it was time for them to join the conversation before the silence got suspiciously awkward. "So," he asked Steve, "where do you two work out again...?"

Three months later...

Steve relaxed against a tree in Brooklyn Battery Park, playing with Alexis' fiery red hair as they both soaked in the warmth and sunlight of the beautiful spring day. Everything around him felt like it was awakening from winter's long, cold slumber: the sun, the flowers, the trees...even the people around him felt they were coming back to life after long months in hibernation.

He could relate.

For the first time since SHIELD had chipped him out of that ice, Steve felt alive. He wasn't just going through the motions of having a life anymore. On the contrary; he was finally beginning to feel like he had a life, a hope, and a future. And all three of those things could only be credited to one person: the beautiful young woman he was holding in his arms.

Steve was in love; he was deeply in love with Alexis, and he knew it. And because of that love, he also knew that they couldn't have any secrets between them if their relationship was going to have a chance. Including his biggest secret. "Hey Lex?"

"Mmmm?"

"You know I'm crazy about you, right?"

Alexis sat up when she heard the serious tone in her boyfriend's voice. "Yeah..." The mix of love and nervous concern in Steve's expression was unmistakable, and it was causing Alexis to worry. "Steve? Honey, what is it?"

Steve caressed the side of Alexis' hand with his thumb, gaining strength from the connection between them. "Lex...I don't want there to be any secrets between us." Alexis tensed up just slightly, but Steve was too wrapped up in his own nerves to notice. "Do you remember how, on the day we first met, I told you that I'm a lot older than I look?"

Alexis nodded. "I don't think you've ever actually told me how old that is," she teased.

Steve swallowed hard, knowing how difficult it was going to be for Alexis to accept what he was about to say. "Alexis, I was born on the Fourth of July..."

"How very patriotic," Alexis teased.

"1922."

Alexis' eyes widened almost reflexively as she considered her boyfriend's confession. "You mean to tell me you're ninety one years old?" Steve nodded. "And when you told me you were ex-military..."

"I fought in World War II," Steve replied.

"Wow..." Alexis exclaimed, dumbfounded. A knot formed in the pit of her stomach as she asked the one question she had to ask. "So how do you look..."

"So young?" asked Steve, completing Alexis' thought. When she nodded, Steve began telling his story. "It took me three different tries to get in the Army. I kept getting rejected."

Alexis raised an eyebrow at that. "You? You practically look like a poster child for the perfect soldier..."

"I didn't always look like this," Steve admitted, blushing. "When I first tried to enlist I was a sickly, scrawny little guy. I was the kind of guy you'd probably call a nerd today. The only way they'd let me into the Army was if I volunteered for a...medical experiment."

"What kind of experiment?" asked Alexis.

"The Army had heard rumors that the Nazis were trying to create the perfect super soldier," Steve explained. "So the Army came up with their own experiment to make sure the Nazis didn't get ahead of them. And their experiment only had one success."

Alexis caught on immediately. "You."

"Me," Steve agreed.

Alexis tucked a wayward lock of hair behind her ear. Her emotions were being pulled in a hundred different directions; shock mixed with surprise, and curiosity and concern mixed with a level of hope she almost found surprising. "And this experiment...is it the reason you look so much younger than your age?"

"To be honest, I don't know," Steve admitted quietly. "Mostly I look this young because I was in a plane crash over the Arctic that kept my body frozen for sixty years."

Alexis' eyes flew open again. "*Sixty* years?!" Steve nodded. Alexis tried to imagine how she would feel if she suddenly regained consciousness sixty years in the future. "That's why you didn't get out much when we first met, isn't it?"

Steve nodded again. "Everyone I knew...everything I cared about...everyone I loved...they were all dead or had lived a long, full life without me in it. I had no idea how to even try to start building a life again. I barely wanted to...until I met you." Alexis squeezed Steve's hand in a gesture of support as he wrapped up his story. "Lex, I know how crazy this story sounds..."

It was then that Alexis did the one thing Steve could never have anticipated. She smiled. "Oh believe me," Alexis countered, shaking her head, "it's not nearly as crazy as you think it is. And it's not nearly as crazy as what I now need to tell *you*."

Steve was starting to feel almost as lost as he had when he first saw the modern Times Square. "Alexis? What is it?"

"Do you remember Detective Esposito? He was one of the guys LT introduced you to at the party."

Steve nodded. "He joined my gym, but I haven't seen him much since then. Why?"

"Well," Alexis replied, trying to figure out where to begin, "the next day, he made me promise something. Something I didn't understand until just now."

"What?" asked Steve.

Alexis pulled Steve to his feet before explaining herself. "Javi made me promise that if things ever got serious between us that I would take you to him as soon as 'I knew.' I guess I shouldn't be surprised that he saw this coming..."

The couple left the park and walked to a nearby alley, giving them the privacy for what Alexis needed to do next. She looked into the eyes of the man she loved, kissing him gently before taking his hands with her own. "Steve...you're not the only one with a big secret in this relationship."

Their surroundings changed in the blink of an eye. Steve turned around in a slow circle, noticing, to his complete amazement, that he was no longer outside. He was in a warehouse, if the high ceilings were any indication, but the sheer numbers of people passing by him were causing Steve to quickly realize that this warehouse was not being used to store things. And as for how he got to the warehouse..."Alexis?" Steve asked warily, "what just happened?"

Alexis swallowed hard, knowing that she needed to explain their mode of transportation...but also fully aware of how hard her next statement was going to be for even her boyfriend to believe. "Steve...I'm a wizard."

Steve's eyes widened in disbelief. "A wizard?"

"Hold out your hand."

Curious, Steve obeyed Alexis' command...then stared, astonished, at the yellow and orange glow of the flame that flickered to life just half an inch above his open palm. His other hand reached out to the flame to try and verify the evidence of his eyes...recoiling only when the heat from the flame started to burn his fingers. "You're doing this?"

"Yeah," Alexis said with a smile. "Pretty cool, huh?"

"I think this is exactly the opposite of cool, Lex," exclaimed Steve. Alexis chuckled as she waved her own hand over the flame, causing it to flicker, then disappear. Steve flexed the fingers of his hand in disbelief, stunned that his hand was completely undamaged. It took him a moment to find his voice again. "Did...did you do that, Alexis?" Alexis nodded. "And you were the one who got us here?" Alexis nodded again. "Where exactly are we?"

"My job," replied Alexis. "At least...it will be, once the paperwork goes through."

"Paperwork?" Steve asked, confused. "Who do you work for?"

Alexis shrugged. "I guess, technically, I work for my dad," she replied. "But my dad and his friends report directly to the President."

Every word coming from Alexis' mouth seemed to be sending Steve into a greater state of shock. "The President..." he exclaimed. "Wow..."

Two new people came down the hallway and entered the conversation. Both men seemed to recognize Steve, although he was only able to put a name to one of their faces. "Detective Esposito, I presume?"

Esposito decided to get all of his cards on the table up front as he shook the hand of his 'kid sister's boyfriend. "And you're Captain America."

Steve raised a curious eyebrow. "You don't look old enough to be familiar with that name, Detective."

"I'm not," Esposito agreed. "But I read memories."

"Ah," said Steve, fighting to accept the brief comment at face value. "So you've known for a while."

"Since the party," Esposito admitted.

"And you never told Alexis?"

Esposito shrugged. "Not my story to tell. I knew you would tell her when you were ready."

Steve nodded, deeply respecting the sentiment behind Esposito's statement. "Thank you." It was then, though, that Steve remembered something else about the former detective. "And you joined my gym because..."

"Just because I respect your history doesn't mean I didn't feel the need to keep tabs on you."

"Point taken," Steve agreed with a chuckle, knowing he might have done the same thing for someone that he cared about. "So do I pass muster?"

"So far." the third man chimed in to the conversation by introducing himself with his hand outstretched in greeting. "Kevin Ryan, Captain. My dad was a big fan of yours when I was growing up."

Steve shook Ryan's hand. "Always nice to be appreciated. And please, call me Steve."

"Okay, Steve," Ryan repeated. "Actually...we were wondering if you wouldn't mind going for a run with us."

"Sure," Steve agreed with a shrug...then stared, open-mouthed, as Ryan and Esposito took off at a speed that Steve knew only one man in the world could match.

Him.

Steve sprinted down the hallway to catch up to the other two men, then joined them as the trio made the industrial area surrounding the warehouse into their own personal jungle gym.

By the time the men returned to the roof of the warehouse, Steve was winded, stunned, confused...and discovering, to his surprise, that he was also the happiest he'd been in decades.

Esposito seemed to be sharing at least some of Steve's enthusiasm. "I have been wanting to do *that* since we first met at the party!" he exclaimed.

Steve turned to his new friends, hoping to start to get some of his questions answered. "So...are you guys like me?"

"Not exactly," Ryan replied as he was catching his breath. "Let's just call it...a different path to similar results."

"So you're not Army?" asked Steve. He turned to Esposito. "You looked like an Army man to me."

Esposito nodded. "I was. Special Forces. But until a few months ago most of us were NYPD."

"So that was your old precinct?" Steve asked, catching on immediately. "The party where we met?" Ryan and Esposito both nodded, so Steve waved his hand around to reference their surroundings and their previous activities. "What is it that you guys do here?"

"That's still being worked out, in some ways," said the fourth man entering the conversation, "but mostly we investigate threats that other agencies wouldn't believe or aren't otherwise equipped to handle." The fourth man handed water bottles to the other three men before extending a hand to Steve in greeting. "Alexis mentioned that she had brought someone over to meet the family, and when she mentioned what you were doing, I figured you could use a drink. Name's Mark Fallon."

"Steve Rogers." He shook Fallon's outstretched hand as he looked around and realized something out-of-place in his surroundings. "There's no entrance to the roof from inside the warehouse, is there?"

"Nope," Fallon replied, shaking his head.

"How did you get up here?" asked Steve.

Fallon took a sip of his own water before answering the question. "The same way you guys did."

Steve was starting to wonder how many surprises were in store for him that day. "So you're like them, too?"

Fallon shook his head. "Yes and no." He tried to size up how much Steve knew before turning to Ryan and Esposito. "How'd he do when you guys were running?"

"Matched us stride for stride," Ryan replied with a smile.

That was the complete opposite of the answer Fallon had been expecting. "Really?" he exclaimed, surprised and impressed by their visitor. When Ryan and Esposito both nodded, Fallon turned his attention back to Steve. "I hope you don't mind me asking, but exactly..."

Ryan cut Fallon off before he could finish his question. "Ever hear of Captain America, Fallon?"

The name registered in Fallon's mind immediately. "*You're* Captain America?" When Steve nodded, Fallon shook his hand again. "That *would* explain it. Welcome to the Network, Captain. It's an honor to have you here."

"What's the Network?" asked Steve.

"The Network is an organization designed to support and protect the descendants of an ancient order called the Guardians of Shangri La," replied Fallon. "Mr. Ryan and Mr. Esposito here are two of the Guardians."

Steve nodded. "How many Guardians are there?"

"Five," Esposito replied. "Me, Ryan, my fiancée Lanie, and Alexis' dad and his fiancée."

"So Alexis isn't a Guardian?" asked Steve.

Fallon shook his head. "Technically, no."

"What's the difference?" asked Steve.

"As far as we can tell," explained Fallon, "the Guardians got hit with a strong dose of pure magical energy all at once, which gave each of them the strongest and most powerful form of their abilities. Because Alexis and I were exposed to lower levels of magic over a longer period of time, we're not as strong as they are."

"Which is why you wanted to know if I could keep up with the Guardians or not," said Steve, trying to catch on to the context of what Fallon was trying to tell him.

Fallon nodded. "I can't keep up with them. Ever. They don't leave me in the dust like normal people, but at full speed they'll outrun me every time."

"So the Guardians are the originals and you and Alexis are...copies?"

Fallon smiled as he took a sip from his water and considered Steve's analogy. "I guess that's one way to put it, yeah." He joined Steve in staring at the skyline of the city around them. "There's a lot of people who volunteer to be a part of the Network, Captain. Good people."

"Normal people?" Steve asked quietly.

Fallon nodded. "I'm sure this goes without saying, but a lot of those people would get hurt if information about our little organization got into the wrong hands..."

Steve waved off the warning. "Mr. Fallon, *nothing* is more important to me than Alexis' safety, I can promise you that. Your secrets are safe with me."

One month later...

The wedding had been everything that Javier Esposito had dreamed of...and much, much more. And now, with the smooth tones of the legendary Frank Sinatra echoing throughout the reception tent, he was having his first dance with his soulmate as husband and wife. "Think we can get Castle to stop time?" he asked Lanie, caressing the smooth muscles of her back as they swayed on the dance floor. "Maybe let us have this moment for a century or two..."

Lanie smiled and played with the hairs on the back of her husband's neck. "Look at the the bright side, honey," she teased, "in about eighty years we get to do this all over again."

"I can't wait," Esposito agreed with a smile. He leaned in to kiss his wife...

The thundering boom of a giant explosion stopped the reception in its tracks. The guests poured out of the tent to investigate the cause of the explosion. Five of the guests seemed to be particularly interested in the cause of the explosion. Beckett, Ryan asked through the Guardian's mind-link, can you see what happened?

Former NYPD detective Kate Beckett was already staring intently to the west, seeing things that none of the other party guests were able to see. There's a column of blue light, she replied, I think it's in Manhattan.

It's in Manhattan, all right, Castle chimed in from the main house, it's all over the news. Some sort of alien attack.

Alien attack? asked Esposito. Why weren't we called in?

Only one reason I can think of, Ryan replied. He reached out with his mind until he made contact with one of the most conspicuously absent members of the Network. Steve? Are you in Manhattan? What's going on?

On Madison Avenue, just south of Grand Central Station, Captain America was catching his breath after saving an office building full of people from a Chitauri bomb. Kevin? he asked through the telepathic connection, Aren't you guys still in the Hamptons?

Yeah, Ryan replied, but we can be there in a flash...

NO!

The intensity of Steve's objection cause Ryan to flinch. Steve? Castle's seeing television reports of an alien attack. What's going on?

Captain America looked up and down Madison Avenue, checking to see if any more Chitauri were headed in his direction. The reports are correct, he replied.

Ryan steeled himself for the upcoming battle. Okay, Castle, go track down Fallon and Katya. We need to get back to Manhattan...

NO! Steve stopped Ryan with an urgent insistence that snapped the younger man out of his train of thought. You guys can't come back to the city. Not yet.

Why not? asked Esposito.

There are other forces at work here, Steve insisted, forces I don't entirely trust...

SHIELD? Ryan asked, remembering a few flashes of Steve's early modern memories.

Steve sent an image of himself nodding through the mind-link. I made a promise to keep your secrets to protect Alexis safe. SHIELD and their associates can help me stop this attack but I can't let you help. Not this time. It would put too much at stake.

Reluctantly, after feeling the depth of Steve's emotions and convictions, Ryan agreed. Just remember that if you don't make it I'll have Beckett bring me across to kill you a second time...

I'll keep that in mind, Kevin, Steve teased through the mind-link. Confident that his girlfriend and her team would stay a safe distance away from Manhattan, Steve turned his attention back to more urgent matters and took off up Madison Avenue to check on the progress of his fellow Avengers.

I really, really would love to hear your comments. I haven't tried to write a crossover because it felt like nobody read them. So the more of you who leave comments (good, bad or indifferent), the more tempted I'll be to keep the story going...