As soon as River felt herself returning to consciousness, she forced herself to feign sleep. She had no clue where she was or who she was with, so she figured a little reconnaissance was in order. A couple of rough run-ins and captures had taught her some important lessons.
"I've never seen her before at all…" said a tiny voice on her right, accompanied by a rustle of some soft-sounding fabric.
An excited voice sounded on her other side: "I know! We should have a—"
"Pinkie, really? Can't that wait until she wakes up?" This voice sounded reasonable, possibly the leader? River made a note to herself that this woman was the one to bargain with.
"Well she is awake! Aren't you, River?"
River filled with dread as she fluttered her eyes, faking grogginess. She moaned for effect and rolled over slightly, actually delaying the fateful moment that she would have to open her eyes and come face to face with what she hoped was just a terrible hallucination.
No such luck, she thought as she was met with the sight of… horses? That wasn't an apt description for her captors. There were four of them, in an odd array of colors. They had tattoos on their flanks. Their snouts were too short for horses, and their eyes sparkled with too much intelligence. One of them, yellow with a pink mane, had wings. They were definitely nothing River had ever seen.
"Good mornin' sleepyhead," said the orange one in a feminine twang. Its… her blonde mane was pulled back and River caught herself wondering for a moment how hoofed creatures managed to do such things.
Alright, time to do this. I'm in a strange universe, surrounded by humanoid ponies. What can go wrong?
"Wh-where am I?" River affected a weak tone, but her confusion was legitimate.
The purple one stepped forward with a smile (how could horses smile?). "You're in my house. Well, my library. I'm Twilight Sparkle." River let more confusion show on her face. "We're in Ponyville."
Oh lord in heaven, it's called Ponyville. And this… girl is Twilight Sparkle. The Doctor probably got a laugh out of this, but River could scarcely believe her ears. She began to open her mouth to ask for more details, but she was cut off by the pink pony.
"And you're River, aren't you? I'm Pinkie Pie, and I'm so so so soooo happy to meet you! I know we're going to get along great, and I can't wait to throw you a super duper spectacular party!"
"How do you know my name?" River interjected before the excited pony could continue.
"Well, I just kind of guessed after I saw your cutie mark!" Pinkie thrust a hoof towards River's hind legs. "And I'm really good at guessing games. You must really like music, too!"
River slowly turned her head towards her rear, eyes widening when she saw the "cutie mark" Pinkie mentioned. A river was seemingly tattooed on her flank, but instead of water, there were blue music notes. TARDIS blue. Suddenly, River remembered why she was here.
"I need the Doctor."
Twilight shook her head. "You'll be okay. I know a lot about pony anatomy, and Fluttershy is a great nurse." She gestured towards the yellow Pegasus, who seemed to try and blend in with the bookshelves behind her. "You don't need a doctor."
"No, no." River shook her head, and shakily stood up. "I need THE Doctor." All the other ponies looked at her like she was crazy.
"Doctor who, sugarcube?" asked the orange pony.
Pinkie Pie started to laugh, and everyone's eyes landed on her. "Oh, sorry, you just reminded me of the colt who just moved into town. Everyone calls him Doc, but his full name is Doctor Whooves."
River's heart skipped a beat. It sounded just like the Doctor; adopting a local name to avoid suspicion.
"Can you take me to him?"
Apparently taking River to the Doctor required more than one pony. Instead of just Pinkie Pie accompanying her, River was surrounded by the four of them. Twilight Sparkle watched River like she was going to fall over any moment, but the others treated her as though she'd been with them forever.
"I don't know much about Doc, other than that he's been staying with Ditzy Doo ever since he got to Ponyville," said Pinkie, bouncing ahead of the group. River felt a surge of jealousy, but composed herself.
"Who's Ditzy?" she asked, keeping her voice neutral.
"One of the delivery pegasi around here," Applejack offered, "though not many ponies trust her with their fragile stuff…" She trailed off, sounding as though she almost said something offensive.
"She's a super duper sweetheart, though, and so naturally she offered Doc a place to stay!"
"Naturally," River muttered. It was rare that the Doctor would stay with someone, as he generally tried to remain in the TARDIS. It was safer for him to not attract too much attention, and he said it was so he didn't trust the wrong people. She knew it was so he didn't get attached. River realized that Twilight was watching her closely again and forced a carefree smile.
"Oh! Here we are!" shouted Pinkie Pie. They were outside a blue and green house, and River wondered again why some things here were clearly not created for ponies. Pinkie knocked her hoof wildly on the door, yelling for Ditzy to come out. There was no answer.
"She might be working," muttered Fluttershy, and River was surprised to hear her speak. She was starting to think the pony might be mute.
Twilight put her hoof in front of her mouth, an obvious thinking habit. "Maybe so. But shouldn't the Doc be there?" She knocked loudly on the door, still with no answer. "I guess we can try again later…"
"Oh! I know! Let's go to Sugar Cube Corner!" Pinkie chimed in, "I know you'll just love it, River." She stuck her face right in front of River and smiled so widely that River could hardly refuse.
"Alright," said River, trying to hide her disappointment.
As the other ponies started to walk away, she remained behind for a moment, staring at the door. Maybe she could will it to open, and the Doctor would be standing there… and then what? There was obviously something wrong with the TARDIS, or he'd be in there already. Plus there was all this pony nonsense. If River was changed, than the Doctor probably was as well. And she didn't know how well she could handle that. Regenerations were one thing, but completely changing into a different creature? That was almost too much.
With one final glance over her shoulder, River followed after the ponies. Not even five seconds after she left, an unmistakable sound came from within Ditzy Doo's house, and the sound of two sets of hooves sounded on the floor.