"You keep all this flying on your own?" The old man crouched near the open panel, fingers ghosting the edge of a coolant manifold, eyes sharp beneath that mess of white hair. He sounded halfway between surprised and impressed. "Remarkable. Especially for someone so young. I don't believe I caught your name, my dear?"
Kaylee wiped her hand on a rag already too dirty to be worth the effort. Her grin was sunshine anyway. "Kaylee Frye. Ship mechanic, miracle worker, and part-time shrink for when the engine's actin' emotional. And you?"
He gave her a sly little smile, one of those half-bows like he'd just been introduced to royalty instead of a grease-streaked girl with busted knuckles. "I'm the Doctor."
She tilted her head. "Kinda got one of those already. He mostly pokes at folks, though. What're you a doctor of?"
The Doctor settled back on his heels like he was enjoying himself. "Oh, this and that. I've picked up a few degrees over the centuries. Engineering, chemistry, time mechanics, anti-gravity ballet—though I doubt that one's relevant here."
Kaylee snorted. "You're jokin'."
"I never joke about ballet." He gave her a wink. "But no, truly—I've been around a while. I learn what's useful. You'd be surprised how often knowing the tensile tolerance of a Hadron matrix gets one out of a tight spot."
She leaned in, eyes catching the light like stars through grit. "So what is it you do, then? Seems like you ain't just some wandering engine groupie."
The Doctor gave a thoughtful little hmm, like she'd asked him whether he preferred scotch or brandy with his after-dinner musings. "That's rather hard to pin down. I travel. I help. I cause a bit of a ruckus, usually. But always in service of something better. Ideally."
Kaylee cocked her head. "You got a whole lotta words to say not much at all, don't ya?"
He laughed, that warm chuckle that made her think of old radios tuned just right. "Yes, well. Habit of mine. And technically, the name's John Smith. But I find it doesn't stick nearly as well as the Doctor."
He nodded toward the open panel, already half-lost in the guts of Serenity. "I must say, your work here's extraordinary. Would you indulge me in a little technical comparison?"
Kaylee's grin widened like a sunrise. "Would I?!"
Which was, naturally, when Mal stepped into the doorway.
"Kaylee, you got that buffer coil re—"
He cut off like a man walking into a crime scene.
The engine room smelled like ozone and too-hot metal, and the pair of them—Kaylee and the old man—were sprawled in the middle of it, shoulder-deep in parts that weren't ever meant to be pulled that way unless you really knew what you were doing. Both of them were greased to hell. The Doctor had ditched his jacket, his wine-red waistcoat all smudged up, shirt frills limp with sweat.
Mal stared. "What in the nine smoking hells is this?"
The Doctor rose smooth as you please, like he hadn't just been elbow-deep in Serenity's innards. "Ah. Captain Reynolds." He brushed himself off as if that might somehow restore the dignity of a man who looked like he'd lost a fight with an oil slick. "I'm afraid I may have encouraged your excellent engineer to indulge me in a technical walkthrough. Entirely my fault, I assure you. Couldn't help myself. Fascinating ship, really—Firefly-class vessels have such character." A pause. "Still, I do apologize for the intrusion. I'll return to my quarters immediately."
He moved past Mal without waiting for a reply, steps crisp, back straight. Mal didn't stop him. Didn't even turn.
Because now Kaylee was standing, too. Arms crossed. Jaw set.
"Don't see why you had to go all hardass on him," she said, voice low and dangerous. "Ain't like he was pokin' at things he didn't understand. Guy listens. Even asked about my stabilization hack on the port vector. Ain't nobody asked about that but Wash."
Mal blinked. "Didn't say he didn't know his way around an engine."
"No, you didn't." She wasn't smiling now. "But you didn't treat him like someone who might."
Mal ran a hand over his mouth, rubbed at his jaw like the words itched. "Look. We got a job comin'. Job needs engines runnin' smooth and nobody fiddling around who ain't crew. Stranger or not, you clear anyone messin' with our guts through me first. Last thing I need is another surprise on a long haul."
Kaylee looked away. Not angry now, just… quieter. Like something folded up inside.
"Yeah. I hear ya, Cap'n," she muttered, already turning back to the engine. Her hands moved like they had their own minds. "Won't happen again."
Mal hesitated. Just a breath. Then nodded, and walked away.
The hum of Serenity filled the silence he left behind.