The Doctor on My Shoulder, Part One by Daniel Roth.
"Mason?" she asked, scratching her head "What's up? I didn't know you were home sick too. And why is there a doll on your shoulder?"
"You know my name?" Mason replied in shock. "But I haven't ever..." Mason's voice trailed off as he peered passed Ana to see an open, brown box sitting on the table behind her. "This is the Doctor." Mason gestured to his shoulder as the Doctor waved. "He's very small. Do you mind if we pop in for a mo'?" Ana, dumbfounded, nodded as Mason was already rushing past her towards the package.
Peering into the box, Mason and the Doctor saw another figurine. This one, though, was decidedly less human looking than the Doctor. Its metal body was cloaked in a long, black robe, its face looked distorted like it had been melted, and a long, reptilian tail stretched out from behind like a metal whip. Tight in its grasp was what appeared to be a magic wand.
Mason carefully placed the Doctor in the box so he could inspect the tiny monster that lay within. "Oh, look at you!" the Doctor said. "Robot mercenary all trussed up for, what, some sort of fancy dress party? What's with the robes, eh? And a magic wand? Seriously? What's that all about?"
"Just looks like a normal toy to me," Ana said.
"Well, he does, doesn't he?" the Doctor said, scratching his head. "Oh!" the Doctor shouted. "I am so thick. Of course he looks like that. Think about it: how else do you trick someone into letting a robot into their house? You shrink them down and make them look like something everybody knows. Oh, that is clever. But what's it all for?" The Doctor brandished his sonic screwdriver. "If I can just work out where it came from," he said, scanning the robot, "then maybe..."
Suddenly, the eyes of the robot opened and glowed red. Its arm extended as it aimed its weapon directly at the Doctor.
"Uh oh, that's trouble", the Doctor said, changing the settings on his sonic screwdriver in an attempt to send the deadly toy back into its slumber. No luck. The wand began to make a low humming sound. "Get out of the way!" the Doctor exclaimed as he ducked and rolled to get out of the way.
A sliver of electrical energy bolted out of the robot's weapon with a loud "Zap!"
With only seconds to react before another round went off, the Doctor swapped settings again. "Come on, come on, come on!" he growled to himself, tinkering with the sonic screwdriver, looking up just in time to see the robot looming over him, ready to attack again.
"A ha!" the Doctor shouted as he leapt to his feet and jammed the sonic screwdriver into the monster's face. The blue, ghostly glow of the sonic screwdriver lit up against the robot's cheek, sending it into a fit of convulsive shock before it finally powered down. "That was close," the Doctor said, breathing a sigh of relief.
"Doctor..." Mason murmured, sounding as though he'd just seen a ghost.
"It's alright now, Mason. The mechanism must've reacted when it detected my alien technology."
"No, Doctor," Mason said again, more forcefully this time. "It's Ana - she's vanished."
The Doctor finally spun around to see Mason standing on his own. "What?!" the Doctor exclaimed.
"That thing," Mason began, "it shot her and then she was just gone!"