Thinking fast, the Doctor galloped to Twilight's front door. "What do you think you're doing?" Twilight gasped.
"Assistant, let's go! Allons-y, hurry up!" Derpy whizzed across the library and was at his side in a second. "It's only a hop skip and a jump from here to the TARDIS," He explained. "Just keep up with me, okay?"
"Got it," Derpy assured and reached for the doorknob.
"Derpy, where are you going?" demanded Twilight. "You can't go outside! Stay here- that's an order."
Once again disregarding the unicorn, The Doctor turned to Derpy. "Ready?"
"Let's just go before I change my mind," She suggested nervously.
"Goodbye, Twilight Sparkle," The Doctor said absently. "Don't make us have to save your life, got it?" The librarian started saying something else, but the Doctor had already thrown open the door. Tugging Derpy behind him, he plunged into the smoking darkness leaving the confused pony and her library behind.
They ran through the fog, holding their breath as the Doctor tried desperately to remember the way they had come. Left here? No- it was a right, wasn't it? Soon, he was hopelessly lost- and worse, Derpy had disappeared. He couldn't hold his breath anymore- the Doctor fell to the ground coughing. What a terrible way to die! He had faced daleks, ruthless humans, quantum-locked aliens and every other terrible thing that was out to destroy him- and he was about to perish from smoke-inhalation in a sugar dusted parallel universe. His vision began to blur and his head spun.
WHOOSH! Something zipped down from the sky and snatched him up seconds before he could lose consciousness. He couldn't believe it- Derpy! She zipped high above the cloud of smoke as her little wings flapped frantically and the Doctor clung on for dear life. "The air is much clearer up here!" She cheered weakly. "But I can't hold out for much longer!"
"Down there!" The Doctor hollered. "I think that's the TARDIS!" Not needing to be told twice, Derpy swooped down and lost her balance. She and the Doctor tumbled onto the hill where the TARDIS was sitting.
Around them, the smoke was clearing- teams of Pegasus ponies were swooping through the sky and gradually clearing it away. The Doctor hopped up and beamed with gratitude at Derpy. "Thanks for saving me,"
Derpy shrugged and flapped her wings eagerly. "That was fun!" She giggled. "I'd do it anytime."
The Doctor's smile quickly melted as he saw the cloud of smoke still billowing up from Canterlot. "Derpy, would you unlock the door, please?" Derpy nodded and reached for her necklace. She turned the key in the lock, and the door clicked open. The Doctor broke into a smile again and ran inside. Immediately he started flipping switches on and pushing buttons. The TARDIS whirred to life as Derpy stood nervously in the doorway. "Close the door!" He said, so loudly that Derpy jumped and immediately pulled the door shut behind her.
She dashed up to the platform to join the Doctor as he pulled another lever into place. "Canterlot, here we come!" he cried, giving the platform a kick and still grinning. "Hang on tight, Derpy!" The TARDIS lurched and shook as the machinery hummed and the tube-like thing in the center glowed in rhythm. Derpy was thrown into the railing and clung to it desperately. Derpy wasn't sure, but it felt like they were moving. Suddenly, they came to an abrupt halt.
"Are we there yet?" Derpy asked uncertainly. In response, the Doctor trotted down to the door and threw it open. From her vantage point, Derpy could only see the Doctor's face drain of color as a chorus of unkind, grating voices reached her ears.
"EXTERMINATE! EXTERMINATE! EXTERMINATE!"