Written in October 2009 for LFWS, my second venture into the fandom. Prompt was simply "dark."

One of These Things is Not Like the Others

"Everyone is a moon, and has a dark side which he never shows to anybody."

There's no warning betraying the change; no static charge in the air, no lightning flash, no sinister music.

It's simple. Sheppard turns around, and in that instant Rodney McKay is sure of two things: there is someone inside his friend who is not John Sheppard, and they are all very, very screwed.

His eyes are dark. Black like coal, like night with no moon. Like something soulless is inside, and Rodney cringes beneath the unfamiliar look.

"Who are you," he asks it, aiming for brave but stammering like it's his first rodeo.

Across the dim lab Teyla turns with a frown but tightens the grip on her weapon as soon as she meets those dark eyes.

Sheppard's mouth quirks, almost there but not quite. "What do you mean?"

"Are you an Ancient?" Rodney persists. He knows the answer – hell, no – but is trying to keep it talking long enough to figure out their next move. His mind is already running scenarios and calculations fast enough to make anyone else's head spin right off of his shoulders.

Ronon's standing obliviously behind Sheppard. "What are you talking about?" he rumbles, gun hanging dangerously loosely at his side.

Sheppard-but-not chuckles. "Yeah, what are you talking about, McKay?" It's condescending, mocking, and just outright evil, and the big guy's finally tipped off that something is wrong.

He takes a step back, gun coming up, but not fast enough. Sheppard's on him like lightning and Ronon's suddenly flat on his back and out for the count. The only weapon capable of stunning without killing is sent out of play, skittering behind a console.

"Ronon!" Teyla is all but pressed against the wall, gun aimed unflinchingly at her friend despite the fear in her eyes.

Damn it. "How did you get in?" Rodney's own weapon is heavy in his poor grip, palms slick with nervous sweat. What did he touch? "What did he touch?"

Teyla shakes her head. "I do not know."

Rodney distinctly remembers instructing everyone, especially Colonel Super Gene, not to touch. But they've seen this type of imprinting before and Rodney knows, depending on the sensitivity of the equipment, an innocent brush of a sleeve against the control panel could be to blame.

He also knows – at least hopes – the effects will wear off if he can keep it talking long enough. Minutes, hours, days. They don't have days. Goddamn alien planets and their secret hidden labs.

"Colonel Sheppard." Lorne's voice crackles faintly over the radio. "Doctor McKay, come in."

Rodney flinches and reflexively reaches for his earpiece, stopped with a look from the imposter.

"It was easy. I might take the time to worry about what was already inside, if I were you."

They always love to hear themselves talk. Rodney fights to maintain eye contact while every fiber of his being in screaming at him to look anywhere else. "I worry about that every day."

Sheppard starts to walk along the perimeter of the room, and two P90s trail his movements.

"Do you? Not that it matters – you'll all be dead in a few minutes."

"Then why aren't we dead already?" Rodney tries to channel Sheppard's strength and snark. "You think we won't pull the trigger to keep you from doing whatever evil deeds you've spent the past few thousand years cooking up?"

Sheppard stops, a good ten feet from the offending console. He tilts his head. "No."

Teyla raises her chin and cocks her gun, causing the thing in Sheppard to smile.

Rodney lowers his weapon. "You're right."

Sheppard opens his mouth, but neither give him the chance to respond, or kill them, or bake a damn cake.

Rodney brings his P90 up and blasts the console to pieces, Tayla joining in.

John collapses, and whoever HE was, he's gone as quickly as he came.