AN/ This is my first TARDIS 100 fic for a long time. I was hoping that The Waters of Mars would inspire me, and it has. This is my response to the end of that episode. Written in the POV of the TARDIS, contains spoilers for the end of The Waters of Mars, but not the episodes after that. The BBC owns it all.

I do not like those thoughts, my Doctor. Those black thoughts. The darkness in your hearts, the arrogance to abuse your powers, to cross the line. You've said it yourself... it's too much power for one individual to have. You are dangerous.

We have learned that we should fear the quiet ones, for they are unassuming, but can be more of a threat than others. You know that all too well, my Doctor. You yourself are a quiet one to be feared. The Oncoming Storm. Remember what we did to the Family of Blood? To the Daleks? To Gallifery?

If you ever decided to turn against the humans, against Earth, that planet we love so much... there would be nothing left. If I were your enemy, I would be very afraid.

You are the best there is. That is why we have survived. We are meant to be a force for good. We keep the darkness at bay.

Now, dark as your mind is, you do not remind me of a noble hero. You remind me of the Master. Really... in many ways you and he are not so different.

This is not you. This is not what should be. Your brain became an iron trap, snapping shut in defiance. I recoiled and withdrew my presence from your mind, the darkness nipping at me and bearing its fangs.

I am angry, but I know it is not my place to punish you. In a way, I am partly to blame. I'm the accomplice. I might have been able to stop you... but I did not. If you had a proper companion here with you, they would have stopped you. You have come close to crossing this line several times already, but they were always there to pull you back, to save your soul. I have told you so many times this is why you need someone, but you have stopped listening to me.

Despite this I must remain loyal, my Doctor. Therefore, whatever punishment that will come to you, I shall suffer it too.

So my anger seethes quietly, and after your mind has relaxed out of its righteous excitement you can sense my ire.

Now you are tense with fear – not for my wrath, but that of the universe.

"Just because they're all gone, does not mean that the laws of time can be broken."

With that thought, I send you a memory. A nineteen-year-old blonde companion - a remarkable young woman you and I can never forget. Her handprint is on our hearts. 1987. A car accident that would result in the death of her father. She ran out and saved him. You, my Doctor, with your deep-sea eyes and leather jacket, were angry and disappointed. She had changed time, against the rules. She saved a life that was meant to be dead. The Reapers came to feed on the Temporal Paradox. I disappeared, trapped, desperate and only just unable to reach you. You and several others were eaten, vanished. The girl and her father had to set things right. He let himself be hit by a car to save the world. He died.

You remember that, my Doctor, and are ashamed.

The Krillitanes gave you the chance to become a god and you said no. Too much power for one man.

"You have forgotten, my Doctor, the rule. Everything has its time and everything dies. You may be the last of the Time Lords and I may be the last TARDIS, but nothing you or I can do can ever change that!"

Even Captain Jack, immortal, may some day run out of lives.

"You were wrong, my Doctor. The line has been crossed."

It is just the tip of the metaphorical ice berg. My Cloister Bell is ringing. The song of the Ood is haunting you. The prophecy foretelling your end at the quadriad of knocks echoes in your mind. The darkness is close. I can feel it, smell it, taste it.

"No!" you shout. Anger, defiance. Not necessarily at me, but at the Universe - that ancient balance you have tried so hard to disrupt, to bend into whatever mould you want. You will run until the end, and when you cannot run any more, you will stand and fight until your body, hearts and mind give out.

The running has already begun. The black thoughts are racing with our hearts. Our song is going to end, and that ending is right around the corner.

Remember this also, my Doctor... I will not abandon you. I cannot. Even if you bring about the end of the universe... on propose or by accident... I will be there.