A/N Welcome, ladies and gentleman, boys and girls, welcome to the saddest installment in my Percy Jackson: Mission Marvel series! (Well, unless Endgame is sadder than Infinity War, which I highly doubt.)

For those who aren't aware, or who just don't like reading the summary, this is the third story in my series, the first being Percy Jackson: Mission Marvel, the second being Percy Jackson: Civil War. Mission Marvel is how the demigods meet the Avengers, earn their trust, and fight at their side during Age of Ultron.

Civil War is during Captain America: Civil War, and how the team splits apart, including the demigods. If you want some more PJ/Avengers crossovers, go and check those out.

There will be demigods that die in the snap, so prepare for a lot of heartbreak.

Anyway I've put this off long enough!

(Percy)

The end of the world started when a wizard strolled into Central Park.

He was walking in the park with Annabeth for their five year anniversary. Percy had turned twenty-one about two months ago, and was now officially living up to his namesake. Annabeth was twenty, her birthday hadn't happened yet. He hadn't even died yet! Tony hadn't revealed to the authorities who Tsunami and Owl really were, so life was good. No quests, no Avengers business, just he and Annabeth hanging out and going to New Rome College.

Then a glowing yellow ring appeared in the middle of the air. It was like Percy was looking into a different world. A guy with dark hair and a flowing red cloak stepped out of the portal.

"Mr. Jackson." The guy said. "Miss Chase. I need you to come with me."

Percy cleared his throat. "First of all, who are you and why should we come with you. Second, why would you need our help? We're just teenagers." Annabeth elbowed him, smiling. Then he heard someone speak.

Jason stepped into the limelight. "Hey, Percy." Percy stared at him. Then his shock turned to anger.

"You're kidding me! You seriously told them? I actually thought you were better than that."

Then outstepped Hazel, Frank, Leo, Piper, Nico, Tony and… Bruce. Percy stared at him. "Uh… hi." Bruce smiled feebly. "Hi Percy." Hazel looked at them pleadingly.

"Come on, Percy. We just need to talk. Something's… something's happening."

Annabeth rushed into the portal and hugged Piper. They hadn't seen each other in a year. The two girls hugged, and for a moment Percy thought he heard a sob escape from Annabeth's lips. But she turned around and looked as stoic as ever, so he figured he must have imagined it.

Percy cautiously stepped into the portal, and it sealed behind him. He and Jason looked at each other warily. Percy stuck a hand in his pocket where Riptide was concealed.

After the disastrous events of the Accords, the demigods split into two groups. Negotiations between Camp Jupiter and Camp Half-Blood continued as usual, and Jason continued to go back and forth between the camps. However, they were significantly colder to the seven from that moment on.

The demigods were probably angry that half of their most powerful warriors were now officially outlaws in the mortal world. Some people backed Percy and some people backed Jason about the Accords. This was partly why Percy chose to mostly live in New Rome and his mom's apartment. It mostly kept the trouble away.

The two sides from the Avengers mostly avoided each other. Percy and Annabeth were still living in New Rome, but Jason, Frank, Reyna, and Piper rarely said hello, though each occasionally caught each other's eyes.

Bruce looked between and looked confused at why they were looking at each other so coldly, but made no comment.

He explained where he'd been and what had happened to Thor. When Percy heard about Thanos and the gauntlet, the words struck an old memory.

"Is he called the Mad Titan?" Bruce stared at Percy. "What?"

"Thanos. Is he called the Mad Titan?" Percy asked more urgently. Bruce looked astonished. "Yeah. How did you…" Percy and Annabeth looked at each other, exchanging a meaningful glance.

"Oh, bad. Oh, bad bad bad." Percy muttered. Tony glanced at Percy.

"Yeah well, the kid will tell us later. Right now we have bigger fish to fry. Bruce, keep going."

Bruce informed them of the Infinity Stones and what Thanos was doing with them.

One of the wizard guys conjured up a picture of the Infinity Stones. Percy had been informed that the guy in the red cloak's name was Doctor Strange, and the other guy was Hong.

"From the dawn of the universe, there was nothing. And then, boom! The Big Bang sent six elemental crystals hurtling across the virgin universe. These Infinity Stones show each essential aspect of existence."

Doctor Strange named all of the stones. "Space." The blue one glowed. "Reality." The red one glowed. "Power." The purple one glowed. "Soul." The orange one glowed. "Mind." The yellow one glowed.

Then Strange made a complicated hand gesture and the locket on his necklace-sorry, locket- opened, and a green stone shone inside of it. "And Time."

Tony sat on the couch, looking very attentive. "Tell me his name again." Bruce stepped forward.

"Thanos. He's a plague, Tony. He invades planets, he takes what he wants, and he wipes out half the population. He sent Loki. The attack on New York. That's him!"

Tony stared at Bruce. Piper paced around the room.

"I don't understand. If these Infinity Stones are such a big deal, then how do the gods not know about them? How do we not know about them?"

"They do." Percy said heavily. "I had a dream about it. Posei-my dad tried to warn me about it. I didn't know enough to understand." Doctor Strange and Wong just stared at the demigods uncomprehendingly.

Percy wasn't about to tell another batch of superheroes about the Greek gods, and just hoped that they would assume they were talking about Thor.

Tony didn't even glance up. "This is it… what's our timeline?" Bruce looked worried.

"No telling. He already has the Power and Space stones. That already makes him the most powerful creature in the universe. If he gets his hands on all six stones, Tony…" Bruce was getting more and more worked up.

"He'll destroy life hitherto undreamt of." Doctor Strange said. Percy snorted. Hitherto undreamt of? Strange gave him a scathing look.

Percy tried to look innocent, but Tony didn't seem to care all that much. He was now stretching on an important looking cauldron. "Did you seriously just say 'hithertoundreamt of'?" Strange raised his eyebrows.

"Are you seriously leaning on the Cauldron of the Cosmos?"

"Is that what this is called-"Strange's fancy-looking cloak slapped Tony on the arm. He looked offended and straightened up.

"I'm… going to allow that. If Thanos needs all six stones, then why don't we just stick this one down the garbage disposal?"

"No can do." Doctor Strange replied. "We swore an oath to protect the Time Stone with our lives." Hong said.

Tony shrugged. "And I swore off dairy, but then Ben & Jerry's named a flavor after me so…"

"Stark Raving Hazelnuts." Strange remembered.

"It's not bad."

"A Hunka-Hulka Burning Fudge is our favorite." Wong put in.

"Is that a thing?" Bruce wondered.

Leo grinned. "I think that 'Blaze Rocky Road' is the best." Jason stared at him. "Seriously?"

"No."

"Whatever." Tony said, trying to reign in the conversation. "Point is-things change." Doctor Strange shook his head.

"Our oath to protect the Time Stone cannot change. This stone may be our best chance against Thanos."

"And still, conversely, it might be his best chance against us." Tony argued.

"Not if we don't do our jobs."

"What is your job exactly, besides making balloon animals?"

"Protecting your reality, douchebag." Percy liked Strange less and less every second. Bruce valiantly tried to bring the conversation back to normal.

"Okay guys; let's table this discussion for later. The fact is we have this Stone. We know where it is. Vision is out there somewhere with the Mind Stone, and we have to find him now."

Jason winced. Piper sucked in her breath. Tony avoided Bruce's eyes.

"Yeah, that's the… thing." Bruce stared at them. "What do you mean?"

"Two weeks ago, Vision turned off his transponder. He's offline."

"What?" Bruce exclaimed. "Tony, you lost another Super Bot?"

"I didn't lose him." Tony protested. "He's more than that. He's evolving."

"Who could find Vision, then?" Doctor Strange asked impatiently. Tony groaned under his breath. "Probably Steve Rogers.

"Oh, great…" Doctor Strange walked away.

"Maybe. But…" Tony sighed. Bruce looked confused at why he seemed so reluctant. "Call him."

Tony turned to Bruce. "It's not that simple. We haven't caught up in a spell, haven't we?" Tony looked around to see if anyone would break the bad news besides him. "The Avengers broke up. We're toast."

Silence fell. The two sides shuffled slightly away from each other. Frank coughed.

"Broke up?" Bruce asked. "Like a band? Like-like The Beatles?"

"Cap and I fell out hard. We're not on speaking terms." Tony explained. He turned to Percy and Annabeth. "Do you guys know where Vision or Rogers is?"

Annabeth shook her head. "We broke off ties with him so it would be less dangerous for us. Technically, we're, well…" She looked embarrassed.

"Criminals." Nico supplied. "We don't know where he is." Tony looked crestfallen.

Bruce stepped closer to him. "Tony, listen to me." He said pleadingly. "Thor's gone. Thanos is coming. It doesn't matter who you're talking to or not." Tony hesitated than pulled out a flip phone. Percy thought it was strange to see Tony holding such a un-high-tech phone.

Jason looked at Percy, looked away, and looked back again. Percy met his eyes unflinchingly. "You got something to say, Grace?" He said, grinning slightly. Jason grinned as well. He walked forward and the two demigods shook hands.

Annabeth smiled at Percy, her eyes sparkling. As of that moment, there weren't any sides anymore, at least not for the demigods. They knew that they would be stronger united than divided.

Tony was about to click the call button on his phone but then he tensed. The demigods froze as well. "Somethings happening." Jason muttered. Tony turned around.

They heard wind whistling through the Hulk-shaped hole in the ceiling. Tony pointed at Strange's hair. "Say, Doc, you wouldn't happen to be moving your hair?" Doctor Strange froze as well.

"Not at the moment, no." He said slowly. They all looked up at the ceiling at saw debris flying overhead. "We're too late." Frank muttered. They all rushed out of the Sanctum.

Outside of New York was complete chaos. Litter was flying everywhere and people were running through the streets trying to find shelter. A woman fell at Tony's feet. "Are you okay?" Tony asked. The woman got up hurriedly and ran away.

A car slammed into a pole. "Help him! Doc, Wong." Tony said. Bruce rushed over to check the driver. "Go! We've got it." Piper ran over and spoke soothing words to the panicked person in the car.

The rest of the demigods ran with Tony to try and find the source. "FRIDAY! What am I looking at?" Tony put on his high-tech glasses. Jason rose on the winds to look and see where all the winds were coming from.

Percy could have put his suit on, of course, but he figured that people were more likely to recognize Tsunami using his powers then a 'regular' New Yorker using his powers.

They rushed through the crowd, securing cars and steading civilians. Jason flew down and landed near them. "Hey guys, I found it." He pointed up at a huge spinning spaceship that resembled a flying donut.

Percy couldn't help grinning. This was the Jason he used to know. "Guess we aren't notifying the United Nations anymore, huh?"

"To Tartarus with those Accords." Piper said, who was examining a wrecked car. "We have bigger problems."

"FRIDAY, evac anyone south of 43rd street, notify first responders." Tony said. Doctor Strange threw some magic winds over the city and the dust cleared. He winked at Tony.

A beam of blue light shone from under the space ship. Two aliens walked out. One looked seriously villain guy, with pasty white skin and he didn't have a nose. The other looked like… a huge guy with a hammer.

"Hear me, and rejoice." The villain guy said. "You are about to die at the hands of the children of Thanos. Be thankful that your meaningless lives are contributing to-"

"I'm sorry, Earth is closed today." Tony interrupted. "So you better pack it up and go home."

"Stone-keeper," The guy said. "Does this chattering animal speak for you?"

"Certainly not, I speak for myself." Doctor Strange readied orange magic shields on his fist. "But you're trespassing in this city and on this planet."

"He means get lost, Squidward!" Tony called.

"Yeah!" Leo agreed. "Get you and your Voldemort-ish nose out of here and maybe I won't light a fire ball right up your-"

"Now is not the time, Leo!" Piper yelled. Voldemort guy looked at the other alien. "They exhaust me. Bring me the stone."

Leo lit up his fists. Frank turned into a lion and roared. Percy was about ready to soak this guy with a wave. Clouds gathered overhead, and lightning crackled. Nico raised some skeletons from the dead. Piper and Annabeth drew their knives, and Hazel disappeared in the Mist.

For a moment, the aliens looked a little freaked out.

A/N And there was chapter one! It was gonna be longer but then I realized how many pages this was and decided to split it into two chapters. On the second chapter I'll do a shout out to whoever reviews. Obviously I can't do it on this one yet, but I promise I will on the other ones!

Hope you liked this, and pretty pretty please REVIEW!