Steve and Bucky visit a grocery store of the future; and Steve, much like a cat, has a lot of fun with the cardboard boxes Tony gives him.

"Whatcha got there, Steve?" Bucky asked, walking into the living room. Steve was coming out of the hallway where the elevator was, dragging two large cardboard boxes behind him.

"Boxes," Steve replied. "Mr. Tony gave them to me."

"He gave you boxes?" Bucky asked.

"Uh huh. See?" Steve continued dragging his boxes into the living room, where Bucky saw a stack of other ones waiting.

"That's a lot of boxes," Bucky said, still not sure what they were for.

"Yeah," Steve agreed happily. "I'm gonna make something out of them."

"Like what?"

"Dunno yet. I have to get the rest of them first."

"There's more?"

"Just three more, down in Mr. Tony's lab."

"I'll go get them for you," Bucky offered, wondering how many times Steve had been up and down from the lab with his haul of boxes. At least he was using the elevator instead of the stairs.

"Thanks!" Steve replied. "I'm gonna go get my scissors and some tape."

Bucky headed for the elevator and Stark's lab, where three more boxes of varying sizes were waiting by the door. "What's with all the boxes, Stark?" he asked, picking them up.

The inventor was hanging upside down from the ceiling, suspended by a pair of robot arms and fiddling with the upper part of whatever that was he was building. "Huh?" Stark looked over, seemingly unaware of Bucky until now. "Oh. Yeah, I got a shipment in. Steve asked if he could have one of them, and I told him to take them all if he wanted." He shook his head. "Lab full of robots and state of the art tech, and he wants to play with a cardboard box."

Bucky chuckled. "Were you never a child?"

Stark narrowed his eyes in confusion for a moment, then gave a shrug of concession. "Yeah, alright. I did play around a lot with the wooden crates Dad's lab equipment came in. Hey, pass me that hammer before you go."

Bucky handed over the hammer and took the remainder of the boxes upstairs. Steve had gotten his scissors and tape, and was currently laid out on the floor in front of his box pile with a pad of paper and his crayons, drawing blueprints for whatever he was making.

"Thanks, Bucky," he said absently, mind on his work.

"You're welcome," Bucky said, dropping the boxes and ruffling his hair. "Let me know if you need help with anything."

Steve was quiet for a while, and when Bucky went back in to check on him, a few of the boxes were piled up in something resembling a wall. "Wait, hold that right there," Steve said. Bucky peered around the wall curiously and saw Steve hastily applying packing tape to the side of a box that Stark's little robot, DUM-E, was holding in place for him. "Thanks, DUM-E," Steve said, patting it on what was more or less its head. "That's a good boy."

The little robot chirped happily.

"Hey, Steve?" Bucky asked later, sticking his head back into the room. The box pile was really coming along—a castle, if he had to guess.

"Yeah?" Steve's head poked up from somewhere inside the castle.

"I'm going to the grocery store to get some stuff for dinner. You want to come?"

"Yeah!" Steve agreed excitedly, scrambling out from inside the boxes.

It was a nice day out, and the store wasn't too far, so Bucky figured they could walk. He still really enjoyed being able to walk places and be out and just…be, without having missions, or chasing or being chased. And it had been a couple of days since Steve had been outside.

He'd gotten used to shortening his strides so Steve could keep up without running out of breath, and he really loved the natural, trusting way Steve's little fingers slid between his metal ones and held on. They chatted as they walked, Steve telling him about the book he was reading about boats, after having finished his space book as well as the one about dinosaurs, and asking Bucky questions about the different sorts of ships he'd been on in the War and for missions and things.

Steve's jaw dropped as they walked into the grocery store. "It's so big!" he said. He'd stopped doing the jaw-dropping thing as much these days, becoming more accustomed to 'future stuff', but it was still pretty cute.

"It is big," Bucky agreed. "So you stick close to me, alright?" He wasn't really worried about that. Back when they were both kids, Steve had been every bit adventurous as Bucky, and though he was still eager to explore, the future was scarier than unknown alleyways of Brooklyn, and Steve wasn't particularly inclined to wander off on his own.

Steve nodded, smiling up hopefully at Bucky as he pulled out a shopping cart. "Can I ride in the cart?" he asked.

"Sure," Bucky said with a smile, hefting him up and inside. He was too big for the little seat in the front, but he could sit down in the basket.

"That's a lot of kinds of bread," Steve said thoughtfully, staring at the variety of loaves on display while Bucky picked up about a hundred tortillas. "What's gluten?"

"Huh?"

Steve pointed at a line of bread loaves wrapped in blue. "Those ones say 'gluten-free'. What's that mean?"

"Oh. Gluten is a thing you get from flour," Bucky said, grabbing several of the regular white loaves, and two of the brown whole-wheat for Thor. "Pretty much all bread has it in it. But they make it special without it for people who are allergic to it."

"Oh." Steve considered this. "I'm not allergic to it, right?"

"Right. With as much bread as you eat—which is a lot for someone as little as you—we'd be in serious trouble otherwise."

"It would be sad if I couldn't eat bread," Steve agreed.

"You kind of look like some sort of story character who's the King of Bread right now," Bucky said with a smile. Steve was currently sitting in the bottom of the basket, all the bread Bucky had grabbed piled up around him and across his lap.

"It's kind of comfy," Steve said, patting the loaves of bread that were propping up his arms like the armrests of a throne. "But bread furniture is a bad idea. I'd eat it all and then have no place to sit."

"It might keep you nice and toasty when it got cold, though," Bucky said with a smirk.

Steve narrowed his eyes. "That's a terrible joke."

Bucky laughed. "Oh, what do you know? I'm hilarious."

Steve couldn't quite keep himself from giggling and Bucky smiled wider.

"Watch out, incoming cheese!" Bucky said, grabbing a packet of shredded cheese and tossing it into the cart. Steve failed to catch it and it smacked him in the face, as did the next five packets, though he did manage to catch the last one.

"Ha!" he exclaimed triumphantly.

They loaded up on jars of salsa—which Bucky did not throw—and bags of tortilla chips. Steve was really starting to disappear under the pile of groceries, but he declined Bucky's offer to dig him out. They got lettuce, onions, and avocados, which Steve enjoyed prodding at curiously.

"Don't poke too hard," Bucky warned him. "You don't want to squish them."

They swung through the breakfast aisle, and Bucky grabbed a box of Pop-Tarts. Steve had introduced him to those and they had been amazing. Now it was time to introduce them to Steve.

"Hey, Stevie, are you out of toothpaste?" Bucky asked as they moved down the toiletry aisle.

"No," Steve replied from behind the lettuce pyramid he was building.

"Are you almost out of toothpaste?" he clarified.

"Yeah, I think so," Steve said. Bucky tossed a box into the cart.

At the checkout, Steve dug himself out of his grocery pile by placing all the items on the conveyor belt in neat little groups—all the chips, all the bread, all the vegetables… The lady at the register thought that was just adorable.

"Oh, he is just precious," she said as Steve stacked up all the salsa jars neatly before climbing up onto Bucky and down again to get onto the floor. "Is he yours?"

"Little brother," Bucky said, looping an arm over Steve's shoulders and patting his arm affectionately. Steve grinned, pleased to be awarded such a title, though really, he'd been Bucky's little brother since, what, about 1920? '21?

They caught a taxi back to the Tower—the groceries were a little much for Bucky to manage on his own, and Steve, while willing, was not of great help with that many bags. They unloaded in the kitchen, and Steve seemed done with his cardboard construction for the night, sitting up cross-legged on the counter in fascination as he watched Stark make tacos and happily smashing the avocados up into guacamole without splattering too much on the counter.

The castle seemed to be Steve's on and off project, something he worked on over the next couple of days when there wasn't anything else going on. He didn't invite anyone else to help, though Bucky was sure he would if they asked. It was nice for him to be able to have something on his own, though, so they all just watched it take shape and commented on how nice it was looking. Sometimes Steve would spend time carefully drawing and coloring in designs on the outside, and sometimes he seemed content to leave it partially decorated and would crawl inside with a pillow and a book.

On Thursday, they got a call from Fury for some sort of emergency mission that just couldn't wait. Bucky got the sense he was tired of them being on the bench anyway, but there were things exploding and people in trouble, so they couldn't really argue.

Since it was an all hands on deck situation, they were going to have to leave Steve there on his own. Stark gave Happy a comprehensive list of Steve's allergies and strict orders to keep an eye on him. Steve wasn't terribly happy about this arrangement—he didn't know Happy at all, though he was willing to trust him based on Stark's recommendation, and he was visibly worried about them all being away.

"Don't worry, Steve," Bucky told him. "It'll be alright. I know Happy's kind of big and scary-looking, but he's a nice guy."

"I'm not worried about me," Steve protested. "There's big explosions and bad robots with guns. One of you could get really hurt."

"How'd you know about the robots?" Bucky asked.

Steve shrugged. "I was sitting outside the door listening while you were all talking about it." His little brow furrowed in concern. "Please be careful."

"I will," Bucky promised, feeling awful for having to leave him here alone. He knelt down in front of him and hugged him. "You'll see. I'll be back just fine."

"Promise?" Steve whispered into his shoulder.

"Promise," Bucky said.

Steve looked up, catching Sam's eye where he stood behind Bucky. "All of you?"

"We'll all be careful," Sam promised, reaching down and ruffling his hair. "We've got a good team. We look out for each other."

"Okay," Steve nodded. He let go of Bucky and backed away. "I don't wanna make you late. Go save people," he said, and he mostly smiled.

The mission went alright, though there was some definite adjusting to the team dynamic with Steve gone. In the heat of battle, they would occasionally forget that Steve wasn't there to call a shot, or to punch his way through something, but they adjusted and worked around it, and they came out of it victorious and not much more battered than they would have been otherwise.

They got back in the middle of the afternoon, and Bucky was wondering if he could get to the medical wing and get that burn on his arm bandaged up before Steve saw it. He was waiting for them, though, at the bottom of the stairs just inside from the landing pad. But…

"F.R.I.D.A.Y., what's going on?" Bucky asked. At the bottom of the stairs was one of Steve's boxes. Steve was inside it, on top of a pillow and under a blanket, Franklin the Second tucked against his chin. There was a stack of books and an empty cup and plate next to the box.

"Captain Rogers is asleep," the A.I. said in a softer than normal voice.

"Yeah, I can see that much," Bucky said. "Why is he sleeping in a box at the bottom of the stairs?"

"And where is his babysitter?" Stark asked unhappily.

"I'm right here, Boss," Happy said, poking his head around the door. "You think I'd leave a nine-year-old up here alone?" he asked, looking offended that they would suggest that. "He wanted to wait here until you all came back, but he kept looking at me like I was freaking him out, so I grabbed a chair and I've been sitting on the other side of the wall. I couldn't get him to budge, so I brought him snacks, and after he fell asleep, I brought him the blanket and the bear."

"Oh," Stark said, mollified. "Alright."

"He's really been sitting here since we left?" Bucky asked.

"Aside from going to get the box and his books, yeah," Happy said.

They decided not to wake him up, so Thor carefully picked up the box with Steve inside and carried him downstairs, while Bucky headed off to the medical wing to get his arm covered up before Steve could see it. Wanda, Natasha, and Sam followed to see to their own various injuries. Steve was unhappily awake when Bucky got back to the main living area.

He was still in the box, but he was sitting up and scowling, arms folded across his chest. "You said you'd be careful," he said, his voice accusatory.

"I was careful," Bucky replied.

Steve shot a pointed look at the bandages on his arm.

Bucky sighed. "People get hurt on missions, Stevie. Even when they're careful. This isn't anything bad; I'll be fine in a day or two." Steve continued to glare, and Bucky sighed and sat down in front of the box. "What's the matter?" he asked gently.

"The matter?" Steve repeated. "The matter is that you got hurt. You were supposed to be okay."

Bucky reached out a hand. "Steve—"

"Til the end of the line!" Steve interrupted, pushing his hand away. "That's what you said! And you said you'd be okay! You promised!" His voice was starting to wobble angrily, and Bucky felt a sharp sting in his chest at the hurt in his little friend's eyes. "What if this was the end of the line?!" he demanded. "What if—If you could get hurt being careful, then what if you got hurt even worse?! What if…" He sniffed. "What if…"

Bucky reached over and tugged him out of the box and into his lap. Steve struggled against the action, but Bucky just hugged him tighter to his chest. "Ssh," he soothed. "Ssh. I'm right here. Feel that heartbeat? Hear me breathing? I'm here. It's not the end of the line."

Steve stopped fighting and curled in against him, latching his little hands onto the front of Bucky's combat vest.

"It's not the end of the line," Bucky repeated. "I'm okay. I'm here." He rubbed a hand up and down his back. "I'm here."

They sat like that for several minutes, then Steve sniffed and raised his head. His bright blue eyes were still watery, but all the anger had drained out of them. "I'm sorry I yelled at you," he said in a small voice.

"It's okay," Bucky said, patting his hair gently. After all the times when they'd been teenagers and young adults and Bucky's worry about Steve had exploded into yelling, it was probably fair. "I know you didn't mean it."

Steve shook his head. "I didn't. I'm glad you're back."

"Me too," Bucky said. "And I really will be okay."

Steve nodded, and they sat there for a little bit longer.

"You okay?" Bucky asked him, once Steve seemed calmer.

Steve nodded again.

"Is it okay if I put you down, then?" he asked. He smiled down at him. "I think I need a shower."

That got a smile out of Steve. "Yeah," he agreed. "You don't smell very good."

"Well, you know, super-soldier, that comes with the super-strength, super-healing, and all that good stuff. But it also comes with super-sweat."

Steve giggled, and Bucky smiled and ruffled his hair.

Big or little, Steve is always going to worry about his Bucky, but Bucky's always going to come home.

Up next, Wanda teaches Steve how to make Sokovian food.