I do not own Doctor Who or its characters
The main difference is that the Tardis is already at the Tower before the Master arrives in the tomb
The 5 Doctors
The Master came up towards the main chamber were Rasillon was buried, his tissue compression eliminator he favoured was useless as it had been damaged by the Cybermen when they had attacked him and the Doctor before. So for a weapon he was temporally using a Cyber gun.
He came into the chamber and saw that three of the Doctors, the first three versions that are were already in there. The humans that travelled with them seemed clustered a short distance away.
But with the he saw the Doctor's granddaughter and the Doctor's Tardis, 'Good' the Master thought 'I can use his Tardis to get back to my own'
He then decided to make his appearance after the Doctor mentioned immortality
He emerged and said as they all turned around to face him
"A thank you gentleman that was all I needed to know. I came here to help to help you. A little unwillingly but I came. My services were scorned, my help refused. Now I shall help myself; to immortally"
The Doctors started to answer back
"Out of the question!" the First Doctor said
"You're hardly a suitable candidate" the Third Doctor said
"For anything" finished the Second Doctor
The Master then levelled his weapon at the Doctor and grinned
"The decision is scarcely yours" The Master said confidently
But his confidence was misplaced, for while his attention had been focused on the Doctor, the Brigadier crept up behind him
But the Master didn't hear him and went on "Killing you once was never enough, but to kill you three times over" and raised his weapon up to kill the Doctors when the Brigadier acted
"How nice to see you again" and quickly the Master turned around to face the familiar human but as he did so the third Doctor went to knock the weapon out of his hand while the Brigadier punched out the Master.
But before the weapon left the Master's hands he instinctively pressed the fire button and let out a shot
And a at a million to one shot it hit someone
Susan cried out and fell to the floor as her stomach was hit, Tegan, Sarah and the other quickly rushed to her side and the Third Doctor pushed through to check
"It bad, it's very bad" he announced and he turned to Tegan and Sarah "Tie the Master up" and the tone of his voice made sure there was no confusion it was an order.
After the two girls had tied up the Master they returned to tend to Susan.
"Come on Susan you can beat this" Tegan said and the First Doctor knelt down next to her
"I'm sorry I didn't come back for you Susan. I thought it was for the best"
"It's alright. I had a life, David and I couldn't have children but he still had a good life" Susan said with effort
Thick red blood flowed out of her body, slowed slightly by pressure being applied by Sarah and Tegan.
The Transmat pad at the other side of the activated on which the Fifth Doctor and another older man appeared; The Fifth Doctor was dressed in his trademark cricketing suit looked dazed and unfocused, the other man wore some kind of black robes a crown encrusted with some kind of crimson stones.
The First, Second and Third Doctors greeted them and the older man said "Thank you gentlemen, you have accomplished the purpose for which I brought you here"
The expressions on the three Doctors faces became instantly those of shock
"He's after immortality" the Second Doctor said
"And you're the one who said there wasn't anything wrong" the Third Doctor said
"Now stand aside" the old man said and Susan felt the psychic waves coming from the crown
The Three Doctors struggled back with their combined strength and the First Doctor said "Join us Doctor we must be one"
It clearly reached the Fifth Doctor because he walked over to the side of his three earlier selves and turned back to face the older man who himself began struggling as the four men combined their psychic strength which was too much and forced the older man to stop.
"You see Borusa" Susan gasped at the name "Together were a match for you" the Fifth Doctor said
"Maybe but you will never overcome me" Borusa said confidently
"We don't need to. Soon Chancellor Flava will be here with her guards, or can you overcome the whole high council" the Fifth Doctor said
"Why not. I'm Lord President and you are the notorious renegades. We shall see who is believed" Borusa said
Then a new deep echoing voce sounded, Susan let out a gasp, she had hear that voice back in school the voice of Rasillon
"This is the game of Rasillon" and a floating apparition of Rassilon's face appeared
Borusa went to claim Immortality and the First Doctor, now knowing what would happen set him up. Borusa ended up a statue around Rasillon's sleeping body and the Doctor explained that the entire game was a trap 'To win is to lose and he who wins will lose' to find out who wanted to get immortality and get them out of the way
"And you Doctors? Do you claim Immortality too?" Rassilon's deep booming voice said
"No" the four Doctors said quickly with the Second Doctor hiding behind the Third.
But the Fifth Doctor stepped forward "My Granddaughter is injured" but he was cut off by Rassilon
"I'm afraid your grand child has already passed the point of no return, however I can offer her a choice" he turned to face Susan "You are still in your first body, if you wish it, I can encourage regeneration without the aid of a Tardis to support the process and stabilise it myself"
"Yes please Lord Rasillon" Susan said weakly barely able to speak now and the founder of Gallifrey nodded
Then all Susan knew was burning
---------------------------------------------------
Everyone stepped back as Susan's entire body was engulfed in bright swirls of red, orange, white and blue light. This lasted for a few seconds and then the light faded away to reveal Susan number 2.
She long red hair and a small round face, her body was about the shape height as Tegan and lips were generous but just the right size.
Susan opened her eyes and they were now a forest green
"Well that was interesting" she said in a musical voice
"Now Doctors it is time your other selves to depart, make your farewells and go. You have chosen wisely Doctor. The one who is trapped in the vortex and the one who is bound have already been freed. Farewell" Rasillon said as his image vanished
The Doctors said goody to each other and the First Doctor said "Susan"
"If you don't mind, I'd like to travel with you" Susan said looking towards the Fifth Doctor who grinned
"Welcome aboard" he said
They all said goodbye and left, The Fifth Doctor narrowly avoiding being made Lord President and with Tegan, Turlough and Susan in tow, ran off into Time and space.
