Leah Stein had wanted to be an astronaut for as long as she could remember. As a child, she'd spent countless night in the backyard with her mother and a telescope, naming the stars and dreaming up stories of the valiant space explorers traveling between them. College had taken her into astronomy and a boyfriend had brought her to the Air Force.

The boyfriend was long gone and she'd been right at home in the Air Force, but when NASA had come looking for pilots for its Ares missions to Mars, Leah hadn't hesitated for a second.

The notification that she'd made it into the final selection pool for the Ares IV mission had come just two days before the Ares III disaster and Mark Watney's death.

It had cast a pall over the entire program and for Leah it had reminded her that space, for all its beauty and adventure, was cold and unforgiving to those who ventured beyond Earth's embrace.

Now, standing on the surface of Mars and looking out over the burnt orange horizon, Leah felt again that sense that she was a tiny part of a much larger universe.

"You good, Stein?"

Leah jumped and turned to find the source of the voice in her comm.

Blair Ortega, the mission commander, stood behind her. Like Leah, Ortega was a military man, but she knew his professional exterior hid a nerd that still saw the universe with child-like wonder. They'd shared enough sci-fi movie marathons on the journey from Earth for her to know that he was just as excited to be here as she was.

The sunlight reflected off the dome of Ortega's helmet, obscuring her view of his face, but she could the small frown pulling at his lips.

"I'm good," she said. "Just thinking."

He nodded. "Well, do your thinking on the way out to the MAV," he said.

"Aye, aye captain," she said, tossing out a sloppy salute. She heard him sigh as she plodded over to one of their two rovers and hauled herself inside.

She settled herself into the driver's seat and took a moment to look out over the construction work her crew was busily undertaking on their Hab. Most of the components were already assembled and had been dropped down to the surface upon the Hermes's arrival in orbit, but the crew still had work to do to make the structure livable inside and fully functional. Solar panels, water tanks, communications arrays, and outdoor equipment storage all had to be set up and tested before their scientific work could begin.

Checking the rovers was one of those tasks. Leah ran through the checklist methodically as the rover booted up. The systems came online quickly and without any glitches — as she had expected.

With a careful touch and a constant eye on the vehicle's rear cameras, Leah backed the rover away from the Hab and pointed it towards the far edge of the Schiaparelli Crater.

She drove the rover slowly away from the Hab, waving at Dale and Fowler, who were setting up their small solar farm, as she passed them. Leah would be out helping them, but Ortega had insisted that one of her first priorities was to go out to the MAV and confirm that it was fully functional and ready for departure.

It wasn't a task at the top of NASA's list — the MAV had been sending routine "all is well" messages like clockwork for years — but Ortega had different priorities. He and Melissa Lewis had served together and Leah knew that he'd been deeply impacted by the guilt Lewis felt for Watney's death.

He was determined that his crew wouldn't suffer the same fate, and he'd driven them all to near madness with safety briefings, and drills, and contingency plans since long before they'd left Earth.

Out of respect for Watney, who'd given his life for these missions, Leah never argued with anything that might keep the crew safe.

So even though getting the Hab to a point where they could conceivably live in it was of vital importance, Leah was spending her time heading out for the MAV site.

It was much farther away from the Hab than would be ideal, but strong winds during landing had put the Hab structure and the crew on nearly the opposite side of the crater from the MAV. Even with the rover, it was nearly a 30 minute trip.

As the MAV rose out of the Martian landscape, Leah furrowed her brow in confusion.

"What the…" she said.

"Is there a problem?" Ortega asked.

Leah jolted in her seat, not realizing that she'd spoken aloud or that her comm was on.

"Stein," Ortega said, an edge of urgency in his voice, "is everything alright with the MAV?"

"I don't know yet," she said, studying the ship as it grew in her windshield. "Something doesn't look normal, but I'm not sure if it's a problem."

There was a tense moment.

"Keep us informed," Ortega said. "You call as soon as you know anything."

Leah nodded absently, still studying the profile of the MAV.

"You got it," she murmured.

It was hard to make out, with the sun shining almost directly in her eyes, but something about the base of the MAV's profile seemed odd to her. Almost… too large.

God, I hope there hasn't been a rock slide, she thought.

She knew NASA had accounted for potential instability in the crater's walls and landed the MAV far enough from them that there shouldn't be any impact. And she knew that the MAV had been reporting a good status for years, but still…

She remembered suddenly a report she had read that there had been some inconsistencies in the MAV's communications almost three years ago. She thought Mission Control had determined it to be a software glitch and performed a remote update.

But maybe Mission Control had been wrong? Maybe it was more serious?

Stop worrying until there's actually something to worry about, she told herself sternly and dragged her thoughts away from pessimism.

Maybe it's just sand build-up, she thought. As long as it hadn't gotten into any critical system, sand dunes shouldn't interfere with the MAV. The crew might have to do some shoveling to make it easier to access the ship, but sand wouldn't be an issue.

But as she finally got close enough that the crater wall and the profile of the MAV blocked the sun's blinding light, Leah realized that what she was seeing wasn't sand or a rock slide.

Her mouth dropped open as she finally registered what the bulky shape at the base of the MAV actually was.

"Holy shit," she murmured.

There was another rover parked at the base of the ship.

"Stein?" That was Ortega again.

"Rover 2 is still parked at the Hab right?" Leah asked, pulling her rover to a stop at the base of the MAV and staring at the other vehicle.

"Stein, what are you talking about?"

"Rover 2. Is it still parked at the Hab?"

"Yes," Ortega said, sounding cautious.

"Stein, is there a problem?" That was Royce Fowler, the crew's computers and engineering expert.

"Problem?" Leah said. "No. Weird? Definitely."

"What's going on out there?" That was Ashley Newman, the crew's flight surgeon.

"Cut the chatter," Ortega barked. "Stein, talk to me. What's going on?"

"There's another rover out here. And it's not ours."

There was a moment of silence, then the comm exploded in overlapping conversation. Leah didn't bother to pick out the individual voices, still staring at the unexpected rover. She unbuckled her restraints in a daze and climbed slowly out of the rover. In the background, she heard Fowler muse about a secret Chinese mission, and Dale counter that it must be aliens.

"Cut the chatter!" Ortega bellowed, drowning out the other voices on the line.

The rest of the crew fell silent.

"Stein," he said, "can you repeat? What are you seeing out there?"

"There's another rover parked underneath the MAV," she said. "And since Rover 2 is still parked at the Hab, this one isn't ours."

"Where the hell did it come from?" Fowler asked.

Leah didn't answer. She'd reached the side of the strange rover and hauled herself up to the look in the cab. It was empty. Abandoned. The whole vehicle looked abandoned. Dust coated the exterior and the wheels were buried in sand. She couldn't see a single track or evidence that the rover had moved recently.

"It's been here for a while," she said.

"Any indication where it came from?" Ortega asked.

"No… but… hang on."

She wedged herself against the unfamiliar rover's cab and reached out to brush the dust away from its sides.

"Holy shit," she murmured. "It's from the Ares III."

"Ares III? Are you sure?" Ortega asked.

"It's got the name on its side," Leah said. "Yeah, I'm sure."

"How in the hell did an Ares III rover get all the way out here?" Fowler asked.

Leah shook her head, but didn't respond. She had no answer.

She hoisted herself closer to the rover and peered in through the cab's dirty windshield.

"However it got here, it's empty now," she said.

She pushed off from the side of the rover and jumped down to the ground. She stumbled a little as her boots connected, still not used to Mars's lower gravity.

"I'm going to check out the MAV," she said.

"Be careful," Ortega said.

"I will."

As she approached the MAV, a flash of sunlight on metal caught her eye. She detoured slightly and found over a dozen solar panels arranged neatly in a semicircle around the MAV's landing struts. She reported her find to Ortega and listened to the crew debate the new details as she brushed dust away from the MAV's access terminal. There wasn't nearly as much dust as she would have expected from something that had been sitting unattended for almost five years.

A niggling suspicion was starting to grow in the back of her mind.

She couldn't put it to words yet, and she didn't try, but she knew that whatever she found in the MAV would be something explosive.

She just hoped it wouldn't be explosive in the explosion way.

The MAV's outer airlock cycled quickly and popped open with ease. The ladder rolled down along its track, settling easily into two indentations in the Martian dust.

"The MAV is responsive and the airlock is open," she reported.

She could almost feel the tension over the comm line. She knew the crew was holding their comments to allow her to focus, but every scrap of their attention must have been focused on her.

She ascended the ladder slowly, doing a visual check of the airlock as she climbed. The airlock's smooth sides closed around her and lit up as the outer airlock door thudded shut. Two of the wall lights looked to have been smashed, but Leah couldn't tell when or how.

She rode the ladder to the top of the airlock and waited while the system cycled and re-pressurized. It felt like hours, instead of the minutes she knew it had taken. She was used to the rapid pressurization capabilities of the more modern airlocks, but thought this airlock might have been operating more sluggishly than she would have expected.

A green light above her head flickered on.

"The airlock is pressurized and the suit is reading a stable atmosphere," she reported.

Fowler swore quietly over the comm and Leah couldn't help but agree. The MAV wasn't meant to have oxygen — at least, not before the Ares IV crew arrived. The ship had been remotely piloted to Mars and had stood (supposedly) empty for five years. There would have been no point in sending it to Mars with oxygen, and it shouldn't have started to make oxygen until Leah or Fowler initiated the oxygen reclamation system during the initial system boot.

"Someone's been here before us," Fowler said.

"Stein, I think you should come back to the Hab. You shouldn't be investigating this alone," Ortega said.

"A little late for that," Leah said.

The inner hatch had already finished cycling and was creaking open.

"Stein—"

"I'll be careful," Leah said. "I'm already in."

She hoisted herself into the MAV, then had to stop and stare. The interior had been completely transformed. Sheets of plastic blocked off most of the small space, threaded between and around the MAV's equipment. Through the semi-opaque barriers, Leah could see that the floor of the MAV was covered in what looked like Martian soil.

In a daze, she pushed aside one of the sheets.

She was right; it was Martian soil, spread across the floor, with tiny, ragged shoots of green emerging from the grit. She gaped at sight, squeezed her eyes shut, and re-opened them, wondering if this was some strange hallucination.

The vision before her remained unchanged.

"Stein, talk to me," Ortega said in her ear.

"I—" she started.

"Don't step on the potatoes." That voice wasn't coming through the comm. It was coming from outside the suit, just behind Leah's shoulder.

She shrieked in surprise and tried to spin around. One side of her got tangled in the plastic sheeting and the next thing she knew, she was sprawled on the floor.

"Stein!" Ortega barked.

"I'm alright," she said absently, staring in shock.

There was a man standing just a few feet in front of her, pressed back against the MAV's outer hull. Blue eyes peered out at her from under long, stringy hair, set deep in a cadaverously thin face. The man wore long sleeves and pants that hung off his thin frame. Blinking at them, she made out a faded NASA patch on one shoulder.

The man stared back at her looking stunned.

"Are you… are you real?" he asked. There was painful hope in his voice.

"Stein!" Ortega barked again.

She ignored him and pushed herself to her feet.

"Yes," she said to the man. "I'm real."

He stared at her, trembling, as she took a step forward. Closer to him, she could make out a faded Ares mission logo on the front of his shirt.

A logo for Ares III.

She peered into his face, a terrible suspicion dawning in her mind.

"Watney?" she asked. "Mark Watney?"

"What?!" Fowler said through her comm.

"Stein—" Ortega started to say.

"Yes," the man breathed. "Yes, I'm Mark Watney."

"Hi Mark," she said. "I'm Leah Stein."

The man—Watney—swallowed hard, eyes flicking around the MAV's interior and hands flexing.

"Are you… Ares IV?"

She nodded.

"Yes," she said. "I'm from Ares IV."

There was a moment of silence, then Leah was stumbling backwards as Watney wrapped his arms around her.

"Thank you, thank you, thank you," he whispered. She could hear him crying through the suit's speakers.

"Stein," Ortega said, "what the hell is going on?"

"It's Mark Watney," she said, wrapping her arms around the man. "He's alive. And living in our MAV."