oOo
The cave was dark now. She had changed back to her normal form, and the poor thing at the restaurant was back. The dimly lit palace was filled with rustling black shapes, their thoughts buzzed through her head. A single, larger one pushed to the center, his voice rang clear in every mind.
It has begun.
oOo
Cadence's dreams grew worse and worse. Sometimes Twilight would turn into a big, monstrous creature with foaming jaws and fangs dripping with blood, and Cadence would wake up screaming for mercy from her old client. Others, Shining Armour would be the murderer, and waking up in his tender embrace would only terrify the poor pony more.
It got worse and worse, until there were only a few hours in a day that Cadence was sane, that the horrible visions didn't plague her mind with their awful, twisted reality. They went back to Canterlot shortly after the visions took over her mind, and soon she fell into a half-coma, too far gone and weary with terror to respond to anything or even eat. Cadence stayed in a continuous state of unrestful sleep, tossing and moaning all day. Shining Armour visited when he could, and when he wasn't with his fiance, his heart was sore with worry, and he lacked concentration.
But as other reports of such happenings began popping up around Equestria, Shining Armour was forced to leave his fiance's side to work out a spell to keep the land safe.
oOo
Cadence stood in a stony tower, lashed to the wall. Her stomach was empty-- no-one had been up for days, maybe weeks. She was to weak to move, all there was to do was hang there and hope somepony helpful might come along before she starved.
She heard hoofsteps on the stairs, and a gruesome, dark alicorn with glowing green eyes and scaly looking, bat-like wings stepped majestically in.
"Wh-who are you?" Cadence asked tremulously. The sheer energy of voicing the simple phrase sent her beyond exhaustion.
"Why, I'm your host, of course." The strange pony seemed to speak in three voices at once, as if many were speaking in a chorus. "I do hope you're enjoying your stay."
"No--"
"Oh, dear, how could I forget? You're chained to the wall, of course you aren't comfortable. I'll come to the hospital instead, yes?"
oOo
And with that Cadence found herself sitting in a white-clad bed in the Canterlot Hospital. The black mare was still by her side, but when Cadence blinked, she found herself staring at her clone instead.
"How did you do that?!"
"Simple. Let me show you." The Cadence-clone swirled into a cloud of green smoke, and then Shining Armour stood next to her, looking at her tenderly. "Hey, there, Princess," he said amiably
"What? No! You aren't Shiny, I know that. Who are you? Don't you ever go by your own shape?"
Shining Armour's eyes flickered, and his features melted into those of the black mare.
"I'm truly sorry I had to invade your mind all these weeks," She-he continued. "But it was only to assure myself that you would co-operate. I'm sure you understand perfectly."
"No, I don--"
"But that's not important, dear. What is important is that you are a vital part of my little plan, in that in order for it to work, I have to get rid of you."
"But--"
Enough! Now farewell, Your Highness" The creature swirled back into Cadence's form, and the changeling's voice turned soft to match hers. "I have a wedding to go to."
Cadence felt herself melting to nothingness, and everything went black.
oOo
Cadence woke up crumpled on the ground with the changeling staring down at her from a dozen different windows above and around her. She looked bedraggled, bruised, and a bit scared, and after staring defiantly at her for a few minutes, Cadence realized she was simply watching her own reflection. She shook her head at her own stupidity, then winced. She'd obviously been dumped here with little or no care, because she had a pounding headache to match all the bruises.
The days, or weeks, seconds, hours, Cadence couldn't tell, as the light was always the same, were excruciating. She managed to find a small, underground river which tasted of metal, but no food. As time passed, Cadence became too weak from lack of nutrients, so she simply lay on the floor, waiting to die.
oOo
"It was what I suspected to be my third day when Twilight burst through the wall," Cadence informed Princess Celestia. She was comfortably supported by her husband, who had refused to leave her side after she had appeared, leaving her no space to be scared of return from the nightmares, or the changeling queen, whose name she now knew was Chrysalis. Twilight stayed with her pretty often, too, but she had the sense to leave them alone some of the time. "She didn't believe it was me, as you know, but I did convince her, and now, here we are, safe and sound."
The wedding had been splendid, as was the honeymoon to their old summer house. Celestia had had something else planned, but after all the trauma with the changelings, both Cadence and Shining Armour agreed it would be best to simply have some peace and quiet.
"We have one more little bit of news for everyone," Shining Armour said, looking at his wife fondly.
"Oh, yes. We do have something else to say." Cadence looked at Twilight and her friends, standing to the left of their Princess. "I'm pregnant!"