"Welcome, Nikola, to the TARDIS!" said the Doctor. He tossed his hunter-green coat onto a coat rack and spread his arms out for dramatic effect. "Is it not magnifisome?"

Nikola Tesla was awestruck by massive room. "It's-"

"Bigger on the inside?" asked the Doctor.

"Actually, I was going to say beautiful," Tesla said. "You didn't really expect me to state the obvious, did you?"

The Doctor pouted. "Most people do. Care to take a guess at how it's done?"

"Well, this is obviously beyond the reach of contemporary science, but I would hazard a guess at the manipulation of dimensional laws?" He stepped forward and surveyed the control panels. As if dared, he reached out to touch the console. It somehow felt more real than he expected. "For a fantastical machine, the façade strikes me as rather anachronistic. Wooden panels, brass fixtures. What are these glowing rods in the center?"

"That would be the time rotor. It goes up and down while the TARDIS is in transit. That's the Teridian detector. This is the vortexilizer. Yonder are the dematerialization notificators. Those are the doors, and there's no panda on any chairs. Care for a ride?" The Doctor smiled and pointed at Tesla. "Trust me my friend, the world might not appreciate you right now, but you will leave an indelible mark on humanity's progress."

"With my work unfinished?" Tesla asked. "Won't going into the future remove me from history and negate my influence?"

"Not if I bring you back when we're done," the Doctor said, already setting the controls. "You're a fixed point. I couldn't take you anywhere dangerous and get you killed. Just a quick peek into the future is as far as I can bend the rules for you. It's the least I can do for your help trapping that Electrolan assassin."

The Doctor was about to grasp the lever that launched the TARDIS when an unfamiliar voice echoed through the corridors. "Stop!"

Nikola jumped when he heard the ring of a cloister bell.

A skinny man in a blue suit and another with an air force jacket emerged from a corridor. Both men looked haggard and smelled of ozone.

The Doctor recognized a future incarnation immediately. "Here we go again."

"What's-"

"Nikola, this is my future self. My people are capable of regenerating a new body when near death."

"So you're crossing over into your own past?" he asked the Doctors. "Isn't that dangerous?"

"Nikola Tesla!" the skinny Doctor surged forward and grabbed his hands to shake them. "Long time no see!"

Nikola looked at one Doctor and then the other. They certainly did not seem like the same man. Appearance aside, they acted nothing like one another. "Just how far into your future is he?"

"To answer your first question, the overlap is very dangerous. It's called a paradox and it can make the universe cry," the long-haired Doctor replied. Then he shrugged. "But it happens. And who may I ask is this?"

"Oh that's Tom," said the skinny Doctor in his form of introduction. "Major in the American Air Force, but don't hold it against him. He's actually an astronaut."

"Well I was," Major Tom said. "Til my ship broke up in orbit. I would have died if the Doctor hadn't rescued me."

"The Major Tom?" the hairy Doctor looked at his future self with a scolding look in his eye. Tom's death was a fixed moment in time. "Haven't you learned anything from my mistakes?"

"What does he mean?" Tom and Nikola asked at the same time.

"I'll explain later," the skinny Doctor promised his companion. "Anyway, we have a problem."

"Oh dear," the hairy Doctor ran his hand over his face. "What did I do?"

"Oh, nothing worse than you've done before…"

"Out with it."

"I accidentally let in a Theran time phantom."

"You didn't," the Doctor groaned. "How big?"

"It's tiny. Lilliputianette. Two and a half years."

"Doctors, please," Nikola said. "I understand there's a threat, but if there's a remote possibility I could help, I need context."

The hairy Doctor said, "It's a noncorporeal creature from the subethers of time and space. It's basically a living fissure in the fabric of reality."

"A living fissure?" Tom asked. "How is that possible?"

"It's a big universe," the skinny Doctor said. "My people call them 'temporalties.' It sent us back here into the TARDIS' past and then folded in on itself. It's roaming the hallways as we speak."

"A living fissure, hmm?" Nikola said. "Doctor, I may have an idea. Is there any way this amazing ship can defy the laws of time internally?"

"As a matter of fact, it can," said the hairy Doctor.

"Then we modify the trapping device we used for the Electrolan to corner it and stretch time forward to starve it to death."

"Brilliant!" exclaimed the skinny Doctor. "Fighting an alien with Nikola Tesla! You really were ahead of your time."

"But what does that have to do with me?"

Tesla turned to Tom. "I'm sorry, but you should have died, yes? The Doctor saved you when he should not have."

Tom looked shocked. "I-I guess so. But what does that have to do with anything?"

"It's attached to you. You, my friend, are the bait."

The skinny Doctor snapped his fingers. "Before trapping it, we can actually reverse its polarity to send us back to where we started. The journey'll age us. We're already two and a half years older, might as well make it five."

Tom made a face. "I just got the taste of fissure out of my mouth."

"Nikola's trap should keep it from following you," the hairy Doctor said.

The skinny Doctor grinned wide. "We just need a name for your new invention. For posterity."

"I was just going to call it the protonilizer," Tesla said. "I don't think I'll bother with a patent. The rest of the world would think I've gone mad!"

"Madness can be fun!" the Doctor exclaimed. "Allons-y!"