This is the 51st anniversary special story. There will be some references to the show and the actors who played the Doctors and companions (with one writer) in the story.

I don't own Doctor Who.

Chapter 1: Back to Coal Hill (again)

It's been a few weeks since the Cybermen invasion on Earth and The Doctor is still devastated that Missy lied that she found Gallifrey but it was still lost. While travelling on his own, the Doctor senses that something strange is happening on Earth and the Doctor went back to Earth straight ahead. But he found out the source of the threat is near Coal Hill School, where his companions used to or currently works there. Knowing that the vacancy for a math teacher is open due to the death of Danny Pink, the Doctor took the job as a substitute teacher as a way to pay respects to the man he helped stopped the Cybermen invasion.

As class is about to begin, the Doctor read the school's textbook to get a better understanding of what Danny is teaching. "Good morning class. My name is Mr. John Smith, but I like to be referred to as Doctor Smith." the Doctor introduced himself after the class enters the room. "Now what was the last thing Mr. Pink has teach you?" the Doctor asked and one student raised her hand, "Yes, miss-"

"Sophie Davison, sir." the student said, "Mr. Pink talked abiut the Pythagorean theorem the last time he was here."

"Ah yes, the Pythagorean theorem. One of my favorite things about math. Now class, as a review, what does the equation of the Pythagorean theorem look like?" the Doctor Asked and another student raised his hand. "Yes, you there."

"The Pythagorean theorem is a^x+b^x=c^x."

"Correct, Mister-"

"Arthur Pertwee, sir."

"Right, Mr. Pertwee. You're correct. Now this next might sound little like a history question, since I'm more of a history person and what not, but who created the Pythagorean theorem." the Doctor asked and another student asked. "Yes, what's your name and what is your answer."

"Carole Ann Ward, sir. The Pythagorean theorem was a created by the Greek mathematician Pythogras, but there other claims that there others that started the theorem way before Pythogras' time."

"Not exactly what I expected, but excellent observation, Miss-"

"Excellent, Carole Ann. Now, I'm going to show you an example and you will answer it orally." The Doctor wrote an equation up on the board and presented to it to the class. "Alright, who can solve this problem? What about you young boy?" the Doctor asked the boy in front.

"I... erm... I can't." the boy said.

"Why not mister-"

"David Agnew, sir."

"Okay David, couldn't get none of your names." the Doctor whispered to himeself, "why can't you solve it?"

"Because I'm not good at math, sir. I'm always struggling whenever I see a complex math problem."

"It's alright. Common people are also having problem with complex math equations as well. The only way you can see it again is if you took a career in the scientific field. What do you want to be when you grow up, David?"

"Erm... an astronaut, Doctor Smith."

"Well don't worry about it too much. With a few practice and some studying, you might be able to get it." the Doctor said to David, "Now, since I'm your substitute for a day, I won't be assigning you homework. But as a special treat, I know a special website we could work on right now."

"We can't." Sophie said.

"Why not?"

"The computers have been acting weird a little while ago."

"But it's not just the school, all of the city's computers have been acting weird too." Arthur said.

"Interesting." the Doctor whispered to himself. "Well then, for the rest of class, just do as much as you can on your books."

Miles away from Coal Hill, a reporter is approaching to a building that appears to be closed. The reason she's going to that place is because there have been many strange reports going the local authorities just ignore it. Others also reported that since the building first appeared, all of the city's computers are starting to act strange.

When the reporter arrived at the building, she found it locked. She peeped into the window and found the place totally empty with the exception of two or three tables. While she was looking around the building, a police man caught the reporter.

"What are you doing here, miss?" the police asked.

"Oh, erm… I just lost my personal belongings that's all." the reporter said.

"I don't believe every word you just said. Can I see your identification."

The reporter took out her id card and showed it to the police man "Sarah Jane Smith, reporter." she said.

The police took a look on Sarah Jane's identification and doesn't seem impressed by it. "I'm sorry, Miss Smith. But I don't have a jurisdiction to let you in this building." the police said.

"Under what orders?"

"Under the orders of the owner of this building, Miss Smith."

"But there's no one in this building. Who would own this building?"

"It's just some old man, Miss Smith. Now move along before I arrest you."

"But-"

"I said move along." the police said as Sarah Jane left the premises.

As soon as Sarah Jane left, the policeman looked around to see if there are other people about to approach the building. At the same time, the policeman is being monitored through a CCTV across the building.

"Commander, shall I obliterate the human 'reporter' from existence?" a figure said as he is monitoring the policeman.

"No, cadet. She is no threat to us." another figure said, "There is another being that is trying to destroy us and he is near our base." The figure typed the coordinates and the monitor showed the TARDIS.

Back in Coal Hill, the Doctor is talking with the other teachers at the teachers lounge. The Doctor looked around and realized that Clara isn't there.

"Erm, excuse me, but can you tell me where Miss Oswald is?" the Doctor asked one of the teachers.

"Sorry, mate. She hasn't been here for the last week or so." a teacher replied.

"Do you know where she is?"

"I heard that she's taking time off for Danny, or something."

The Doctor then think that Danny came back from the Nethersphere and that he's with Clara. Suddenly, a man in a suit and tie entered the room and made an announcement.

"Everyone, we are please to announce that the Chairman of the Governors has made an announcement in Coal Hill." the man said and everyone, besides the Doctor, are murmuring. "May I present to you, Mr. Ian Chesterton."

After the man announced his name, Ian Chesterton entered the room and everyone applauded. "Oh, it seems that Coal Hill is still home to me." Ian remarked

While Ian is talking, the Doctor is thinking about his times with Ian Chesterton. He was one of his first companions to travel with him. Now, he is growing a little older and currently leading a school. When he was done making his announcement, Ian is shaking to every teacher in the room. When he reached to the Doctor, Ian felt something strange about him.

"I say, didn't I remember you from somewhere?" Ian asked.

"No, erm… I was the substitute caretaker a few months ago. Now, I'm a substitute math teacher. I'm John Smith." the Doctor said as he and Ian shook hands.

"Oh, now I remember. You were the craziest caretaker I've ever met. Why are coming back here?"

"I, erm, just wanted to do something good for the kids at Coal Hill. I have a degree in mostly everything. That's why I'm a school teacher and not a Caretaker this time."

"Well that's very good, Mr. Smith. Dedication to Coal Hill is just what we needed here."

"How is your family life?"

"Well, it's perfectly fine. I'm married to a girl name Barbara Wright, who used to teach here like I did, and our children, Verity and Terrence, are great kids."

"I'm sure they are."

"Well I better be going back to work. The school is not gonna lead itself, you know." Ian remarked and then left the room with the other teachers, leaving the Doctor behind in the room to think.