Don trudged back through the aisles, sighing with exhaustion. He and Sarah had spent the better part of three hours working through the plane’s occupants, collecting blood samples with hastily scavenged equipment and testing for any presence of the virus. He rejoined Sarah in the small section of the plane they’d commandeered as their lab and leaned against the wall, wondering what time it was. Sarah glanced up from her laptop. “You let Director Woods know?” she asked.

He nodded. “All passengers confirmed nanite free.”

“Did she say what our next move is?”

Struggling to hold back a grimace, he shook his head. From a logical standpoint, he understood Olivia’s approach of keeping their course of action secret until they were on the ground. The risk of spreading panic through the plane was too significant and potentially dangerous. However, he hated lying to a trusted colleague and friend, particularly one to whom he owed his life. Grasping for a change of subject, he motioned to the laptop. “Reviewing notes?” he asked.

Sarah’s forehead furrowed. “Checking a discrepancy. I hadn’t had time to look at the latest samples we took from Marcus Meier before…” She trailed off, her jaw tightening.

“Go on,” Don urged.

She resumed her typing. “It didn’t seem critical to review them at the time, since the vaccine took precedent, but these scans don’t make sense. Here.” She turned the computer around and showed him a view of three distinct images. Two showed enlarged pictures of the nanites, while the last one was clear.

“This first image is the initial sample we took of Mr. Meier to confirm the presence of the virus,” Sarah explained. “Take a look at the second. Can you see anything different about the nanites?”

Don leaned in and compared the two images. “There’s an extra protrusion on the bodies of the second,” he noted. “Some kind of… rounded bulge.”

Sarah drew back the computer and moved her finger across the touchpad. “Sort of like this?”

When she showed it to him again, another image was on the screen, displaying a different nanite, slightly sleeker with nearly double the limbs and that same bulge on its frame. “Whose sample is this?” he asked.

“Yours,” Sarah said. “From when you were infected.” Her expression grew tense. “I think that bulge is what houses Eden’s enhanced programming controls.”

“But Meier never left quarantine,” Don said. “How could the extra parts suddenly appear in nanites from a previous generation?”

“They may possess the ability to remotely upgrade themselves,” Sarah suggested, clearly nervous about the possibility. “If that’s the case—”

“Then Marcus Meier could have become another one of Eden’s agents,” Don finished.

“Possibly… but here’s where I get lost. Look at the last image, the one showing no nanites present. That’s Meier’s latest sample. We didn’t give him any variation of the vaccine, so what happened to the virus?”

Don met her worried gaze as a feeling of confusion crept through him. A dozen, half-formed possibilities entered his mind all at once. “Maybe… the adaptations to the older generation of nanites shorted them out, or they possessed a lifespan that we weren’t aware of. But if that means we left another innocent behind…” he groaned.

“I’ll keep reviewing the samples,” Sarah promised. “Maybe there’s something more we’re missing.”

Don nodded, feeling fatigue and hunger starting to set in. “I can’t think straight. I’m going to see if the galley has anything to eat. You want anything?” he asked, straightening.

“Bottled water, if there’s any left.”

With a nod, he started down the central aisle, dodging around moving people. About halfway to the galley he spotted Connor hunched in one of the seats and motioned for the young man to follow him. He found a tiny point of clear space away from the other passengers and leaned in close. “We might’ve discovered something strange about the nanites.”

“Everything’s strange about the nanites,” the tech expert muttered sourly, then winced. “Sorry, didn’t mean to snap. I… really don’t like confined spaces.”

Don waved away the apology. “This many people crammed in a jet would make anyone claustrophobic. But focus for a moment, I need your help with something.”

Connor nodded. “Shoot.”

“Could the nanites be advanced enough to… retrofit themselves?” Don asked.

Pursing his lips, Connor shrugged. “Theoretically, but… wait, what do you mean?”

Don described what he and Sarah had seen in Mr. Meier’s scans as best he could, watching as Connor’s expression turned thoughtful. “It sounds like the overall design of the nanite didn’t change much in the second version,” he said. “Eden could have built self-modification systems into the original template, with the idea of essentially patching the earlier generations once improvements were available. No idea what could cause them to just vanish though. That doesn’t fit any previous behavior I’ve…” He broke off with a pained gasp and grabbed his forehead.

“Are you all right?” Don asked.

“Really bad headache,” Connor said through clenched teeth. “My skin feels hot too.”

Don pressed his palm against Connor’s forehead. Intense warmth, like a high fever, radiated through his skin. The young man’s eyes darted nervously, and his breath came in rapid bursts. A knot of dread tightened in the pit of Don’s stomach.

“Connor,” he said softly, “were you outside when Eden attacked with the vir—”

“It was only for a minute!” Connor insisted with panic. “I-I went out for a smoke break. I didn’t want to say… I thought you’d put me in quarantine! I could barely handle being in that room once before. Shit, what’s happening to me?”

“Calm down,” Don said, his thoughts racing. “Listen to me. Your blood sample came back negative, so you aren’t infected. There has to be another explanation, just let me think.”

Connor continued to pant so quickly that Don feared he was on the verge of hyperventilating, even as a strange lethargy overtook his expression. “My mom… always told me… smoking was gonna kill me…”

“You’re going to be fine. Come with me, I want Dr. Douglas to take a look—”

A lanky arm shot out, and long, knotted fingers grabbed Don’s throat. He reeled back, fighting to pull away from the grip and Connor’s terrifyingly blank stare. A few people nearby noticed the struggle immediately and broke Connor’s hold. Don’s pulse hammered as he watched the young man violently shove the others back.

“What the hell is going on?” a familiar, angry voice demanded.

Connor’s vacant gaze snapped to Mike. He threw a man more than a head taller than himself across the plane and rushed the agent, one hand grabbing the gun at his waist.

“Mike, he’s infected!” Don yelled in warning.

As Mike struggled against Connor’s grip on his firearm, his free hand grasped at his belt, finding the hilt of the sword Sarah had given him. As Connor inexorably bent the gun toward Don, Mike got the blade free and drove it through the tech expert’s chest. A wave of screams rippled outward from the crowd.

To Don’s horror, Connor didn’t stop moving. He ignored the metal blade jutting from his back and knocked Mike away. Several people reached for him, but he deflected the grabs and charged down an aisle, the sword still transfixing his body.

He’s going for the pilot…

Don ran after Connor, his longer legs allowing him to close the distance between them, but the lanky tech was already fighting with the handle to the cockpit door. With a hard sprint Don launched himself at Connor, and they both went down in a confused tangle of limbs.

An unbelievably strong arm hurled him on his back. Connor straddled his chest and wrapped both hands around his neck. Agonizing pressure built around his throat, denying his attempts to draw breath. In a panic, he clawed at Connor’s wrists and fingers, but nothing could break the implacable grip. He stared up in fear at the blank mask of the tech expert’s face as his vision started to blur.

Sharp, stinging pain lanced through Don’s body as the hold on his throat loosened. Choking and gasping, his muscles fighting any attempt to control them, he saw Mike above him, jamming a handheld stun gun into the nerve cluster on Connor’s upper shoulder. With stiff, jerking motions, Connor lashed out and knocked Mike away. The pain abruptly cut off.

Slowly, Connor twitched his way to his feet, pulled the sword out of his chest and raised it high, blood dripping from its tip to spatter on Don’s shirt.

“Don, get away from him!” Mike shouted.

Scarcely able to think straight, Don pulled his legs up and curled into a tight ball. The sword came streaking down, but suddenly Mike was there again, the stun gun’s prongs buried under Connor’s ribcage. The infected man’s body went rigid while he stared at Mike with something like blank incredulity. One jerking inch at a time, Connor angled the bloody sword closer and closer to Mike’s body. The tip sliced into the agent’s leg…

Then fell, along with a convulsing Connor, to the floor. Mike pulled Don away from the twitching body as a shocked silence filled the plane.