"50th Anniversary" was the title of the 2013 Comic Relief Special, used both to raise money for the charitable organisation and also to celebrate 50 years of Doctor Who. It lasted in total half an hour, shown in six-minute segments throughout the night. It is known for featuring four different incarnations of the Doctor, as well as voice-acting from three others
The Eleventh Doctor stumbles about the Tardis, which is violently shaking. He mumbles something about the Banana daqueri and then looks at some dials. As if in a sudden revelation, he takes a sink plunger from under the console and attaches it to main console, which seems to stableise it. The Tardis phone rings.
"No. Not yet. It's too early."
He runs round and answers the phone.
"Hello? Is that Geoffery? Oh, I hope it's Geoffery..."
He flips a switch and a familiar voice echoes through the Tardis; that of the Eight Doctor.
"You know who I am because I presume you've already called yourself and remember doing so."
"What? Oh yeah. I thought I'd get the other one."
"What 'other one'?"
"Nevermind now, spoilers remember."
He flips a few switches, types in a formula into the typewriter and presses some buttons on the monitor. The engine roars into life and then fails.
"No no no! I don't remember mentioning this, at all, in any way."
"What is it?"
The Tardis gives a final shake before the engines fail. The Doctor sighs and switches off the intercom, and walks outside. He walks out into a dark alley. It's just rained. He clicks closed the doors and walks down the alley. There are more Tardis engine sounds, but slightly more ricketty. A darker blue Tardis forms in front of him. The door swings open and the Eighth Doctor strolls out, using his key to lock the door.
"You jammy sod, you still use a key!"
The Eighth Doctor swings round and looks in fear at the Eleventh.
"Is that... my nose?"
In another alley, a battle-worn Tardis forms into a corner. An edwardian-dressed Ninth Doctor stumbles out, confused and addled. He reaches into his tuxedo for the Sonic Screwdriver and brings out the blue-tipped version. He uses it on the water traces dripping from the roof.
"Tarserus. Tarsereun drug-water. Not seen that in... a while. I've been here before. I'm sure of it. In this suit too."
He stumbles down the alley, muttering to himself.
The Eleventh and the Eighth walk together down the alley into a quiet street. The houses are in the shape of pyramids, the water dripping down off of horizontal poles.
"Where are we, exactly, old man?"
"Tarserus. You tell me that. Or I tell you. It's confusing."
"Tarserus, eh? Home of the drug-waters, and the great central distortion. That's probably why we're all here."
"Yes, the Tenth should be popping up at the end of that street down there right... about... now."
A Tardis roared into being where the Doctor was pointing. Out walked the Tenth, in a blue jacket.
"Is it me, or have I been here before?"
The Tenth walked up to the Eleventh and looked him straight in the eyes.
"Do I turn into you?"
"Yes, you do. Now, I remember from being you that I had to go somewhere and so something rather urgently."
"Oh yes. Thanks."
The Tenth Doctor then sprinted down the street, with the other two in hot pursuit.
The Ninth has wandered into a different street. There's a triangular hole in the ground, with a deep tunnel leading far into the ground. He only just notices a young blonde man across from him, in the darkness.
"It's pretty deep down there, isn't it?"
"Yes, it is."
"You wouldn't want to jump into that, would you?"
"It leads down to the Great Distortion. It's a space-time black-hole, it tringulates the spacetime around this planet. We need the drug-water to stay sane."
"Yeah, well. What would happen if I did jump."
"Your atomic structure would be divided in three. Every atom in your body would form the shape of a pyramid. You would know pain for all eternity."
The blonde then jumped into the Great Distortion, his scream echoing back up.
The Ninth is scanning the edges of the entrance to the Great Distortion with his sonic screwdriver. He's mumbling.
"Hmm. It's made from Tarsereum steel, it's immune to deterioration from Artron Energy. If I'm right, then judging by the pitch and echo of that scream, halved and then divided by the time... he can't be dead. There's something else in there."