The Doctor where on his Tardis reading some books about pony anatomy, some time ago he talk with Derpy about his natal place his planet Gallophrey, since that moment he put his hooves in action.
He has a plan, he close the book of Advance Pony Anatomy in a backpack grab some notes and faster than the wind get out of his Tardis, the door closes with the wind he creates. '
He run straight toward Ponyville like a crazy stallion to Twilight Sparkle castle in his way he crashes with some ponies "Hey, be careful" shout one, "Why don't you look where are you going?" say other "Hey Doc, where is the fire?" ask Diamond Tiara giggling.
The poor pony only say "Sorry, I'm so sorry, out of my way!" it was so fast that couldn't stop his march so literally collided in the castle door.
Spike reply to the noise "Doctor! What's the matter?" the poor pony where in the floor and blab some words without any sense he shake his head and then without any time to spend say "IsthereTwilightSparkleIneedtospeakwithher" Spike make some signals trying to calm down the crazy horse "Yes, she is here, what do you want to do? Kill yourself?" ask the baby dragon, "Well yeah, there is something like that involve" reply The Doctor, Spike was frozen with his reply almost like an statue so The Doctor grab him and move to close the door.
Once inside he start again a race to follow Twilight he was sure at this time she's on her library so he keep running into some corridors, both of his hearts going to explode, some more corridors and then finally get into the library.
Twilight were surrounded by piles of books when she hear some noises The Doc couldn't stop and a great pile of books fall in his body, instantly Twi get up from her pillow and assist the one who where under the pile of books, she uses her magic and hooves to reveal the poor tan pony complaining about the pain.
"Doc" she exclaimed "Why the hurry? I mean is not usual to see you in that state" The Doctor make a last effort to get out of the rest of the books "You'll see Princess, I have a plan but i need your assistance to make it work" Twi was really surprised and excited he only count with Derpy for all so she was really grateful finally she's going to assist him "Of course what's about then?" she levitated and sit him where she was before in a comfortable pillow soft and warm. "You'll see is complicate and I don't want Derpy to know this before everything is done" he say meanwhile he comb his hair "Ok i'm all ears" precede the princess "tell me your plan" The Doctor grab the anatomy book and his notes he stopped when he found a chapter that talk about the heart.
"I'm so happy here in Ponyville that well i'm decide to stay but Miss.Princess Twilight Sparkle you'll see I want to live like anypony and in this condition is practically impossible as you can see dear where i came from we have two hearts" Twilight got closer to check his notes.
He point with his hooves some illustrations he has and take her hooves to touch his chest she got a bit nervous "What's again your plan?"
she finally ask again "In order to stay with the mare i love, to be finally with Derpy, i have to make a major surgery" when he finally end Twilight with an horror face ask "What? Are you crazy that's never was made before!" the stallion hug her hooves and cry "Please, help me princess in this condition I'm like immortal and I'm going to see how Derpy grow old while me, me..." he cry even more the princess make appear a tissue with magic and dry his tears finally she understand "Count with me"
He jumps and hug Twilight grab his notes and the book and place all in his backpack "I need you in the Tardis tomorrow morning then well see how it comes out everything" he grabs the princess hug her and say "Thanks for this" another set of tears roll down his cheeks and with a bright smile set his steps out of the library "Hey Doc, you don't need my help inside the Tardis it could be hard to make it by yourself" shout Twilight he stop his march look at her and add "Don't worry I manage to make it work I create some sort of energy to charge it for the last time, don't worry about that" he say with a fresh air.
The Doctor was really happy to have the help of the princess by his side he feel like a feather with an smooth step leave all his things in the Tardis and goes to Derpy's home. He was standing still in front the door an incredible fragrance comes from that house, Derpy weren't so skilled but when she know The Doctor was coming to have breakfast she cooked like a goddess, the smell where so spectacular that he where only there shaking with nervous finally he decided to knock the door. The gray pegasus open the door "Doctor!" she hug him and he was trying not to melt "I don't expect you so early it's so good to see you please come to the kitchen the muffins are almost done" he hurry to the kitchen and try to take a muffin "No" Derpy smack his hooves"There are still too hot, why don't you wait 'till I serve the tea... silly Doctor" and giggles.
The Doctor blushes a bit "Ah! Miss Derpy where is Dizzy?" Derpy giggles a bit more "She is camping with the class you are worse than me Doc" The doctor shake his head that was the hurry he want to make his plan before she returns provably it goes much worse if she was here with them.
At last everything was ready to have a great fist Derpy were serving some tea with milk when "You know Miss Deprs, I want to live today like it was my last day"
Derpy where moving some muffins to the desk she reach it before she makes a disaster and sit on a chair next to The Doctor "Why do you say that?" The Doc take a muffin and continue "I don't know, i want to do something different do you have any plans for today?" Derpy moves her head "Actually i rent some movies to see" she knows that The Doc doesn't like being around Ponyville they spend the weekends indoors watching movies "Forget about them Miss, what ponies in this place do in a lovely day like this?" Derpy smile finally he decide to go outside and he where curious about life in Ponyville "Well we can go to the local carnival