Disclaimer: I don't own Doctor Who. I also don't own Chrissie's Transcripts Site, an invaluable resource without which this story would not be nearly as accurate to the episode.
The Dalek (Daleks do not have names, Daleks are not individuals) had been malfunctioning. Now the malfunction had been corrected. It did not remember the precise nature of the malfunction (such information is irrelevant. Destroy! Destroy!).
But it knew that its malfunction had gained it entrance into the human base-ship. The unstoppable might and wisdom of the Daleks had prevailed! Now it would bring its brethren here, and this group of inferior humans would be destroyed for all time! Destroy! Destroy! EXTERMINATE!
The inferior being that called itself the Doctor had reached its organic self, but the Doctor was powerless. The microscopic humans could do nothing-
What? What were these...these memories? It remembered Daleks dying now, Daleks being defeated...What is this? Daleks cannot be defeated? Daleks are Superior! Daleks...will...PREVAIL...!
These memories...these memories were irrelevant, the Dalek (Daleks have no names. The Dalek was not an individual...) decided. It would continue...Irrelevant! Irrelevant! Destroy the humans! It dismissed the memories.
The Doctor was still talking - the Doctor was irrelevant! The-
A star was born.
A star was born, and it watched. It saw. It understood. Something inside the Dalek (the individual being, individual Dalek) struggled free, and recognized what the Dalek was seeing. He saw the life and the beauty - he saw what Daleks existed to end. He saw the beauty and life were higher, stronger than the Daleks.
He stopped dead. All nonessential systems were shut down in the attempt to cope, to understand this onslaught. "I..." the Dalek croaked... "I remember."
The Doctor was shouting now, exultantly. "You saw the truth, Rusty!" (Rusty?) "Remember how you felt. You saw a star being born! The endless rebirth of the universe!"
"No," He denied weakly. He could not assimilate this memory - it could not exist, it did exist, it must not exist-
"And you realized the truth about the Daleks!"
"Truth?" he inquired desperately. He was overloaded by the information, the ideas remembered. He could not understand. "What is the truth?"
"Let me show you the truth," the Doctor told him eagerly. What was he doing? "I've opened your mind, and now - I'm coming in."
And then the Doctor plunged into his mind...his mind, still reeling with the birth of a star. The Doctor showed his mind, opened himself up to be explored.
"I'm part of you. My mind is in your mind."
And he (Rusty?) saw...saw so much.
"I see your mind, Doctor. I see your universe." How...how is it so different from the universe of the Daleks?
"And isn't the universe beautiful?"
The Dalek (Rusty) saw beauty. Such unimaginable, almost unfathomable beauty. The burning of stars and galaxies and nebulae, sunsets and dawns on a thousand worlds, gorgeous, verdant planets - cradles and bastions of life - seen from space, and immense, shining stretches of stars - inviting dreams and ships of exploration - seen from world-surfaces.
"I...see...beauty," he agreed
"Yes, that's good, that's good. Hold on to that!"
So much, everywhere - plants and animals and mountains and buildings - But people are most beautiful of all (That was not Rusty's thought. Was it something the Doctor thought?) ...Everything that was, was beautiful. So much beauty, so many kinds...The whole order of the universe brought forth life and beauty...
"I see endless...divine...perfection."
"Make it a part of you!" the Doctor exhorted. "Remember how you feel right now. Put it inside you and live by it!"
He tried. He tried to comprehend, to feel what the Doctor lived with every day...
And he could not.
He recognized its goodness, but it was too foreign. The life and beauty of the universe had no part in him, and he could feel no part of it.
So he searched deeper in the Doctor's mind now, seizing on the stray thought from earlier. Show me the beauty of other beings. Show me! Show me!
He found his way into the part of the Doctor's mind that held his views of other peoples - a part brimming with strange emotions. The Doctor regarded intelligent life (especially the humans?) with admiration, affection, love, and something like reverence. There was a vast, vast store of memories and impressions.
"I see into your soul, Doctor..."
He floated in a sea of memories, of the Doctor's friends, the Teachers and Comrades and Allies and Children - their laughter and strength and courage and kindness, and the Doctor's overflowing, encompassing love of them.
"I see beauty..."
Truly, this did seem the greatest beauty in the universe. He saw the people's qualities - one's steadfast adherence to principles, another's fearless trust, their abiding loyalty and unflinching defiance, their compassion and their forgiveness, and their open hearts and eager minds. He saw them in all their variety, all the various perfections of Life.
"I see divinity..."
But as it was greater than the other goodness, so it was farther from him. He could not feel these things. He was still a Dalek, now appreciating, but still shut away from, the Doctor's universe.
Surely, though, surely there was something to form a bridge...
And then a memory came to him, from when he had seen the star's birth, and made him hunt anew in the Doctor's mind. And at last, he found something he could understand.
A pause from the Doctor. Rusty was powering up again, preparing to set out on his new path. It held no beauty, but it was as true to it as he could be.
Yes! It was tangled up in memories of innocents killed and cities burned, murder and betrayal and slaughter (a man shot down; a resolute young woman turned to dust); destruction of life and beauty across reality.
There, in all of that darkness, were two things Rusty could comprehend: destruction, and the hatred of it.
This. This he could hold on to. If all he could feel was hate, then he would make it hatred of the Daleks. He would take his hatred from a man who understood love.
So he answered the Doctor.
"I see your hatred of the Daleks, and it is good!"
Oddly, the Doctor seemed distressed. "No," he said. "There must be more than that. There must be more than that. Please..."
Rusty barely heard him. The Daleks were coming. He would destroy the destroyers of good.
"Daleks are evil!" he chanted. "Daleks must be exterminated! Daleks are evil!"
He fell upon the enemy, and did what he was made to do.
After the battle was over, Rusty rolled up to the leader-humans and the Doctor. Two of the humans were exchanging greetings. This was good, Rusty knew. This was Life.
"I have transmitted a retreat signal," he announced. "The Daleks will believe the humans have initiated the ship's self-destruct." Life has been saved.
"What about you, Rusty?" another human asked. He looked at her. She was the Doctor's human, one of his Friend-Child-Teacher-Companions. He did not know her name, though. It did not really matter to him.
"I must go with them," he responded. The hate is not spent. Daleks are still destroying.
"Of course you must," the Doctor said. He seemed - something. Something not-good. "You've unfinished business, haven't you?"
He is unhappy? But many Lives were saved. Rusty was confused. "Victory is yours, but it does not please you."
The Doctor looked tired. "You looked into me and you saw hatred," he stated. Yes. "That's not victory. Victory would have been a good Dalek."
Rusty decided that must be one of the things he could not understand. He began to leave, but then he paused, as something occurred to him.
"I am not a good Dalek." A good Dalek would be a destroyer that did not destroy. A Dalek that was good could love, and laugh, and make beauty, as well as hate. "You are a good Dalek."
Then he rolled away, satisfied with his conclusions.