The First Law of Time specifically states that Time Lords are not to cross their own time streams. This has happened on more than one occasion. However due to the remaining Time Lords, other than the Doctor, being locked in an impenetrable time bubble the laws of time no longer apply.
Due to recent events of the Doctor's companion Clara Oswald, every previous incarnation of the Doctor has met Clara in some way or another. She went through the Doctor's own time stream on Trenzalore, where the Doctor lay buried, to save him. In return he saved her, however something was happening. Something that could not be undone.
Because of Clara's efforts the Doctor was saved, but time had been rewritten for the Doctor on a massive scale. When such a thing happens to a Time Lord, Time Lord protocol mandates that every incarnation of the Doctor is collected in the same pocket outside of time and space to discuss what has happened and what further actions are required.
All across time and space every Doctor was being contacted. From 1964 with his first incarnation stretching to 2013 where his eleventh incarnation was, every Doctor in their T.A.R.D.I.S. was receiving a message on their screen. "This is an urgent message for all of the Doctors. It is vitally important that you listen carefully, for once!"
Back in 2008 the tenth doctor hit his console. "Eh, who's there?" he asked. "Who is speaking?"
In 1964 the first doctor turned slowly to face the screen. He too was in shock as was every doctor who was experiencing the same thing at that moment. "Each of you are being transported out of time and out of space in regards to Time Lord protocol mandated by the First Law of Time."
From 1964 to present day each incarnation of the Doctor was brought to a room that had no windows and no walls. All but a single oval table was in the room. Twelve chairs were positioned around the table. A man stood at the head of the table, a man no Doctor recognized. He was tall and slender. He had short brown hair and bright green eyes with a near-pale complexion. Before anyone could speak the man raised both hands in the air. This was Gallifreyan for letting one know they had the floor to speak, also a slight sign of trust amongst the doctors.
"As I am sure by now you are all aware of why you have been summoned, and that all of you just so happen to be the same though in different bodies at different points in time," the man said. "I am equally positive that you are not aware of who I am. Allow me to explain."
"This is not possible," the eleventh doctor said standing up.
"Aye," agreed the ninth and tenth doctors. "The Time War ended everything that had to do with the Laws of Time." The previous eight doctors looked around in confusion. They were unfamiliar with the Time War and what that meant to Time Lords.
"Doctors, please!" the man said. "I insist you are all here for a reason, lest I would not bring the eleven of you together."
"I'll tell you what this means," the fifth doctor began, "it means that whoever is the current me, rather us, has crossed our own time stream. And I'm curious as to why."
"Here here!" several of the doctors agreed.
"Would you care to explain, doctor?" the man asked the eleventh doctor. Every eye was upon him.
The eleventh doctor sighed. "Well as you all know the doctor does not like to travel alone. I met a woman by the name of Clara. But she wasn't just a woman, she was an enigma. She died the moment I met her, and then once more after that. I had no idea what to make of her."
"Enough to make any one of us curious, go on," the first doctor pressed.
"A prophecy was foretold, one regarding our greatest secret," the eleventh doctor said. "I was forced to visit Trenzalore."
A collected gasp was heard. "Do not tell us you went!?" the third doctor exclaimed.
"I had no choice. My friends had been kidnapped, one even murdered," the eleventh doctor explained. "I saw our tomb. But it was too late. A horrendous villain treacherous enough to rival even that of the Master entered my time-stream. I was dying, we were all dying. You should have all felt it too. So in order to save me my companion Clara sacrificed herself and jumped in after the Great Intelligence."
"And in so doing she saved us, all of us," the ninth doctor said standing up to place his hand on the eleventh doctor's shoulder.
"But at what price, doctor?" the second doctor questioned.
"Once Clara jumped into our time-stream she split herself so that every time the Great Intelligence attempted to murder us, she thwarted him. She was born in different eras and times. She was the girl born to save the doctor," the eleventh doctor explained. He sighed and slumped into his seat.
"I don't understand," the third doctor said. "That can't possibly be what's gathered us all here."
"I'm afraid it is," the first doctor said. Everyone's eyes turned to him. "Tell us, doctor. What does this Clara look like?" The eleventh doctor raised an eyebrow.
"Oh come now doctor, don't tell us that you've forgotten how to communicate with fellow timelords, or in this case yourselves?" the third doctor questioned.
"I'm afraid it's been some time," the eleventh doctor said.
"Your first incarnation is right, doctor," the man stated. "Show them Clara and perhaps then they will understand."
"Hold on a minute there chap," the tenth doctor said. "There are eleven current doctors gathered in this room and one man whose identity we are still unsure of. Why should we trust you?"
"That is of minimal importance at this moment," the man replied.
"It is important if all of us are about to put our heads together," the tenth doctor said. "That is when we are most vulnerable."
"Agreed," said the ninth. "Tell us who you are. Because to be perfectly honest, we have no reason to be here. The Time War ending should mean that the laws of time no longer apply, even to our previous incarnations."
The tenth doctor looked around. "It's a long story, really," he said.
"The Time War between Time Lords and the Dalek race did not put an end to the laws of time," the man replied. "It simply put an end to those who control the laws of time. They are still in place and all of you know that when such a change to a Time Lord's timeline occurs, this is protocol," the man said.
"Who are you though?" the fourth doctor asked.
The man sighed. "Fine, doctors. If you must be aware I am the eleventh regeneration, the twelfth doctor, as it were."