Ultimatum

I didn't waste my time trying to figure out how Dr. Demented got into the Archives. He could manipulate space and time to is will. He had engineered a virus which magically turned humans into teleporters. He could get into the Archives.
I did wonder why nobody noticed him. He was out of my range of vision, out of Lucy's. How did he know where to teleport so he wouldn't be seen. Did he remember from when he was me? It was a definite possibility. Or maybe he had been watching our whole conversation unfolding. He was probably capable of that.
Which reminded me of my predicament. "Are you saying that it is a problem that I will not kill you?"
"It is. For both of us." He cackled.
Did he want to die? How was that possible? And why couldn't he arrange his own death. I began asking the question, but answered it while the air was still moving through my lips.
He had protections prevent that. I had put the protections in myself. I couldn't take my own life. Physically incapable. My mind would freeze first. I consulted my code. I was absolutely capable of killing Dr. Demented. In the I-can-contemplate-the-concept-without-my-brain-deliberately-changing-the-subject sense.
Dr. Demented couldn't kill himself. And he would destroy anyone who tried to kill him. But he couldn't kill me. Because I was him.
That left me of with the impossible task of ending the life of a space god.
So now I knew why I had to kill him. I just didn't know why he wanted that. "Why do you want that."
He was the Master of Time. But it took him an eternity to respond.

"I used to be magnificent. You know that. You are magnificent, and I used to be you. I reached such incredible heights of brilliance, of power, of passion and happiness and success. Planets worshipped me as a benevolent god. And rightly so. Other feared me as a punisher  from the depths of space. And rightly so. Still others thought of me as an all-knowing teacher. And rightly so. One planet thought I was all three. They were kind of messed up." He paused for breath. During the length of that pause, I analyzed every word, every twitch on his eyes and face. I'm sure he did the same to me, assuming he was still in command of his faculties. Verbal communication was so slow.
"I had power, and knowledge. And I had love. Nimue. One of the Computer People. She had shown me so much. And I had shown her so much. It was wonderful. We created greater and greater technologies. We worked wonders upon the stars and planets and the depths of oceans and the genomes of viruses. But I grew sick. My mind decayed. My wits lost some of their sharpness. My power diminished just a little bit. But it didn't matter. I had Nimue to support me. Until I didn't. A minor miscalculation. I was responsible for the death of a loved one."
As he breathed in, I had plenty of time to think. What if I had miscalculated? What if I had allowed the Puzzlemaster to kill Vera? And what if I had caused Lucy's death. I remembered her previous 'demise'. It was terrible. Imagine how it must have felt for those two, who must have spent millennia together.
"I sank deeper into madness. My mind left for hours, days, millions of years at a time. My power dimmed. I grew miserable. It tried to use my time powers to reverse my mistakes. I only made things work. The bugs in my brain, the ones that you have already inextricably placed into your brain, only grew more damaging." Dr. Demented fingered a ring on his hand. A quick spectroscopic analysis showed that what remained of Alex was trapped inside.
"Now, I am a wreck. I had to compose this speech beforehand, and store it in twelve different parts of my brain. Most of the copies are damaged beyond repair. Now you know how I have become a living mockery of myself. Why I am insult to myself and my wife. Why my life is not worth living."
I took in his speech. For about a microsecond. "No. I do not understand. Life is about power and knowledge. You still have an incredible amount of both. I'm sure you've searched for a cure. But search harder. Enlist my help. Enlist your own help in a multitude of eras. Ask the Computer People. Someone must know how to fix you."
Dr. Demented wanted to say something sarcastic. Something to the effect of 'Ask for help? Never thought of that!' But he couldn't find the words. Instead, he stuttered in Chinese.
He launched into another prepared spiel. "You are reluctant to kill your future self. Very well. I will incentivize you. First, with gifts. You will find your home on Earth restored, filled with marvelous inventions to help you. If you kill me, they are yours to keep. But there are also consequences for failure. In twenty-four hours, if I am still alive. I will kill Vera in front of you. Twenty-four hours after that, I will torture Lucy to death before your eyes. Twenty-four ours after that, you and I will be that last living things on planet Earth."
The Doctor snatched up Lucy in a vicelike telekinetic grip. And then he disappeared. I began my journey to Earth. My mind was roiling with a million futile ideas.