Author's notes: This is my Once Upon A Time In Mexico story. I've already finished it, so I'll post the first three chapters and if I get positive response then I'll continue to update - I should manage a chapter a day. This is a SandsxOC, and is pretty similar to the movie (especially as it's told in third person) but with the addition of my CIA agent, Sadie Carter. Hope you like it!

Disclaimer: I do not own Once Upon A Time In Mexico, its characters or its plot. All I own is Sadie and Mr Cooper.

Chapter 1 – Mariachi

"You asked to see me sir?" asked Sadie Carter, a twenty five year old, half-Mexican beauty.

"Ah, yes," replied Mr Cooper, interrupted from his thoughts.

Mervin Cooper was the in charge of all the field agents at the CIA – Central Intelligence Agency. Out of all the agents, Sadie was his favourite, not just because she was beautiful. She had long chestnut hair, and sparkling green eyes. Her skin was quite tanned, due to her Mexican blood and the time she spent in the sun. She was incredibly tidy, her hair was always perfect, so was her make-up, and her nails were always neatly filed and manicured. Even on missions.

She was a brilliant agent for many reasons. Her looks often tricked people, so she could get what she wanted, and she was very smart. She was also incredibly agile and her reflexes were amazing.

"You've heard about the plan to assassinate the Mexican president, haven't you?"

She nodded.

"Not that I know anything about it, they're not saying much on the news."

"Well, General Marquez has been hired by the drug lord Barillo to do the job. We want you to stop this from happening."

She nodded again.

"Anything else?" she asked.

Cooper shifted uncomfortably. He was hoping he wouldn't have to tell her this, but she could always tell when something wasn't being said.

"Actually yes. As well as stopping the assassination, we want you to keep and eye on the other agent who's out there."

"There's another agent? Who?" she shrieked.

"Agent Sheldon Jeffrey Sands," he sighed. She'd have found out eventually anyway.

Sadie felt herself tense at the mention of Sands. She hated him with all her heart. He was thirty eight, preferred to be known as just Sands, never hesitated in killing anyone and was also quite good looking. Not that that mattered. There was just something about him that infuriated her, and she didn't know if it was his big head or those good looks.

"So you're only sending me because, as usual, he can't do his job right?"

"I'm afraid so."

She sighed.

"You're a brilliant agent Carter. One of the best, in fact. But it's going to be very dangerous, so we decided to send someone older and more experienced. You were our first choice, I assure you. Please, you will still go won't you?"

She smiled. She liked Mervin, and would do whatever he told her to do.

"Why isn't he doing his job right?" she asked curiously.

"That's what we want you to find out."

She rolled her eyes.

"So you don't actually know anything about what he's doing?"

"No," admitted Mervin. "But we have our suspicions."

"So explain what I'm going to do," said Sadie, who always had to know the full picture first.

"Go to Mexico, arrest Marquez before he kills the president, arrest Barillo, but make sure you follow him first, find out exactly what he's doing. Oh, and don't forget to check on Agent Sands."

He passed the file over to her.

"Got it sir. When's the flight?"

"Tomorrow morning. And remember, they plan to kill the president on the Day of the Dead."

A day later, Sadie found herself on the private jet to Culiacan, Mexico. She was going over the files, getting the mission straight in her head. They'd booked her into a small hotel on the outskirts of town, half an hour away from the airport.

By the time she'd had to fasten her seatbelt for the descent, she had her plan. She was going to pretend to be a tourist, and for that reason had packed t-shirts saying things like I Love Mexico and Love Your Life. Today though, she was wearing a white shirt and jeans. When she got there she'd drop her stuff off at the hotel, then get something to eat (she was starving). Then she'd find out information about her targets – including Sands.

As she stepped off the plane, she was overwhelmed by the sudden heat. No one had mentioned anything about the heat. She tied her hair up into a ponytail and put on her sunglasses.

The CIA had also arranged a taxi to take her to the hotel, which she was very welcome for. She didn't feel like walking three miles in the midday heat.

The hotel was…small. But, Sadie didn't need luxury; she just needed somewhere to sleep. Her room was on the first floor, and smelt like pee. But there was a clean bed, a shower and a toilet, so she couldn't complain.

She left her case in her room, and started to look for somewhere to eat. Her stomach was grumbling, and she really didn't care where she ate. Luckily, it was just a five minute walk to the shops and restaurants, through narrow alleys which were much cooler than the streets. The first place she found was a smoky café, which was quiet and seemed to serve meals.

Sitting at a table near the door was a man. He had dark shoulder length hair and wore a dark brown jacket. He looked remarkably like…

"Sheldon Jeffrey Sands!" she cried, sitting down opposite the man. He looked up. He wore blue-tinted sunglasses and black leather gloves and appeared to be more attractive than the last time she saw him

"Sadie Carter?" he asked. "What are you doing here?"

Before she could answer, a man pulled up a chair next to them. He wore an eye patch over his right eye.

"You didn't tell me there'd be a girl," the man muttered.

"I didn't know myself," replied Sands, looking at Sadie.

She rolled her eyes and pulled off her sunglasses so she could see the two men better.

"I never heard of him," said Sands, now acting like Sadie had gone.

"Who?" asked the man.

"The man you recommended."

"The guitar fighter?" he asked, disbelieving. "He wiped out a couple of towns single-handedly. A real nut-job. Yeah, you probably heard of him. You just didn't know it was him they were talking about. You should meet him."

A waitress interrupted their conversation (which Sadie had been listening to closely) carrying a plate of food. She looked at the three of them, wondering whose it was.

"Me, that's mine," Sands told her, smiling.

She set down a plate of some sort of pork dish and a glass of something before walking away, allowing them to continue their discussion.

"Just as long as I'm not the guy who has to make the introductions," the man continued. "Were you in Mexico during the Barillo cartel massacre?"

Sands looked up from his food.

"No," he said, shaking his head.

"That's when I first heard about him. He was a legend. They used to say he was the biggest Mexican they'd ever seen. That was total rubbish," he chuckled. "He was five nine, five ten, tops. That's no record, but bigger than most of us. But Marquez, that's a different story."

Sadie perked up at the mention of Marquez. She might need the information this man was giving away.

"Marquez," he carried on. "General Marquez. He was powerful, dangerous. He really had it in for this Mariachi, you see. They called him 'Mariachi' because he used to carry this guitar."

"A guitar?" asked Sands curiously.

The man nodded.

"Believe me; he really knew how to play it too. He even used it to shoot a couple of guys. Specially made for him, a gun fitted inside."

Both Sadie and Sands raised their eyebrows.

Seeing the looks on their faces, he shrugged.

"Look, this story is well-travelled. It might have picked up some embellishments on the way. Just read between the lines…Now, he may not have been the biggest Mexican ever, all right. But she was as deadly as she was beautiful."

"There's a girl?" asked Sands, looking up again.

"Oh yeah, there's a girl. When he'd run out of ammo, she'd take over. The most drop-dead gorgeous woman you'll ever see. That's where all the trouble began. See, she was with Marquez. And when Marquez saw that she was with the Mariachi, well, he went crazy. He hunted him down and fought Mariachi to the death. And then she…put a bullet in his heart. Only, he didn't die. I don't know what happened after that."

"Would you like some?" interrupted Sands, gesturing to his pork.

"No," answered the man. Sands looked at Sadie, and she shook her head. "Maybe Marquez caught up with them, or the cartels," said the man. "But like I said, the man is a myth, a legend. And if he's still living, he's the one you want."

"Well," started Sands, removing his glasses. "That is truly unbelievable."

"Well, I'm not big on telling stories. Where's the money?" he asked, suddenly turning serious. "That's the reason I'm here."

"I couldn't find a briefcase small enough for ten thousand dollars in cash," Sands said, picking a Clash of the Titans lunch box up off the floor.

"I offered you fifty. Why'd you say no?" he asked suspiciously.

The man checked the contents of the box while shrugging.

"I'm not a greedy man. Not looking to get rich quick. Besides," he said, shutting the box. "Fifty thousand is a lot for what you wanted me to find out, you know. You may just as well kill me as give me all that money, right?"

He chuckled. Sands watched him closely, smirking.

"But ten? Ten thousand is civilised. Ten is something we both can live with."

"Ten might still be too much," Sands told him, raising his eyebrows.

"You'd kill me over ten thousand dollars?" asked the man, clearly not worried. "You wouldn't dare."

He stood up.

"You wouldn't dare."

"Yes I would," whispered Sands when he had gone.

Then he looked around him, checking that no one was around. Satisfied he placed a hand on his left shoulder and pulled. Sadie heard a mechanical hissing sound, and then the next thing she knew, the arm was off, revealing what she guessed was his real arm underneath. He placed the false arm across the table and pulled his own arm out from under the table, putting the gun his hand had held inside his jacket. He then picked up a leather bag from next to him and stuffed the arm inside – with some difficulty. Finally he zipped it up and picked up his sunglasses, ready to go.

"Aren't you going to speak to me?" asked Sadie.

"I've decided to pretend you don't exist."

"So you don't wanna know why I'm here?"

"Well, now you mention it…" he said.

"I'm here for the same reason you are, and to make sure you do your job properly."

He chuckled.

"They don't trust me?"

Sadie shrugged.

"They didn't say. But, obviously, you're not doing your job right, because you can't seem to do it alone."

"I am doing it alone!" he cried.

"Then who's the guy?"

"That's Belini, got some information for me."

"You paid him to get you information, I see. So what are you going to do with this 'Mariachi'?"

"That," he said, standing up to go. "Is none of your business." Then he walked out.

Sadie picked up her phone and pressed in Mr Cooper's number. He answered on the first ring.

"Mr Cooper, it's Sadie Carter."

"Wonderful, how's it going?"

"Well, I've met up with Sands."

"What's he up to?"

"He's payed some guy to give him information on this guitar hero. What he's gonna do with the 'Mariachi', I don't know."

Mr Cooper sighed.

"He can never do a thing alone," he muttered. "I have to go now Carter, but call me when you have more information."

"Yes sir."

She put her phone away, considering what to do next. Eventually she decided to visit the Barillo estate, and find out what he was up to. Then she'd see what happened when and if Sands met this Mariachi guy.