AN: I'm assuming that Susan must have returned to Gallifrey at some point.
I should also mention that I don't own anything.
Fallen
The Doctor walked down the corridor in the heart of the citadel with long purposeful strides. People stepped aside to let him pass, muttering greetings and shooting him admiring glances. The Doctor just wanted to yell at them. They had never accepted him, his own people had shunned him, even exiled him.
But now he was back in the Time Lords' good books again. Now that he felt like everything that he was, was slowly dying, leaving nothing but the empty shell of a man, now he had the respect of his people.
The war had made soldiers of them all, comrades-in-arms, fighting together and dying together. The Doctor's steps slowed a bit, as memories threatened to overwhelm him. He had seen kids, barely out of the Academy, already in their last body, and age-old men fighting side by side. They all had the same look in their eyes – hollow and dead.
The Doctor faltered in his stride as he turned a corner. This was it. He was about to destroy another life – the life of someone he loved. He lifted his hand to open the door and paused. His hand trembled slightly, as he remembered the battlefield – smoke and blood and screams and death. He shook his head, as if trying to shake off the bitter memories, and opened the door.
The woman sitting at the desk looked up and her careworn face broke into a smile. "Grandfather," she said, getting up and hugging him.
"Hello, Susan," the Doctor said slowly, unable to hug her back. She didn't know it yet, but in a few minutes his beloved grandchild would hate him.
Of course it took her half a nanosecond to realise something was wrong. "What is it," she asked softly.
The Doctor lowered his head. If he'd had any tears left, he would've cried. Why exactly had he insisted on doing this? Why had he pulled a favour with the High Council to be the one to tell her? But now it was too late to be a coward.
"Susan," he rasped, surprised by the roughness of his own voice. "Your son …"
He had to catch her as her legs gave out. Slowly he lowered her to the ground, where she sat with an empty look on her face, as if her mind had fled. "Susan," he whispered, trying to through to her.
A shudder ran through her body. "Alex! Please, no," she moaned desperately. "My baby. Tell me you're lying, tell me you're wrong." She curled in on herself, as if she was physically hurting. Her eyes bored into the Doctor's, beseeching him to take back his words.
The raw pain in her eyes was scorching him. The Doctor felt his hearts break a little more with every one of her pitiful sobs. In his mind's eye he could see a much younger Susan, clinging to him and crying over a broken toy. He shuddered, as he realised, he had gone from breaking toys to breaking people.
"Susan," he whispered. "I'm sorry. I was there but I couldn't safe him … no one … Arcadia was lost … and A-Alex …" He gently touched her arm, trying to comfort her.
She flinched, as if he had hit her. "Don't," she begged in a broken whisper. "Just don't."
Even with his otherwise infallible time sense, the Doctor had no clue how long they stayed like this on the floor in her office – Susan curled into a ball, sobbing inconsolably and he kneeling next to her, as if in penance for his sins. Her grief was cutting through him like a razor, shredding his very soul.
Suddenly Susan calmed. She pushed herself up and wiped the tears from her eyes. Something had changed. The spark had gone from her eyes. She had done, what they all did these days – she had taken the pain and turned it into cold fury. "I'll kill them," she hissed. "And if I have to throttle every filthy little Dalek with my own hands, I'll kill them all."
"No," the Doctor breathed. "Please. Not you." The only reason he had agreed to fight for them, had been to keep the war far away from innocent people like his granddaughter.
Susan pushed herself up and looked at him with dead eyes. She had been broken by the worst possible pain – the Doctor knew only too well. "I have to get back to work," she said in a cold, flat voice. "And I'm sure you're needed elsewhere too."
The Doctor nodded. "I'll be here whenever you need me, Susan," he whispered, as he turned to leave. He walked back to his TARDIS, wondering why people kept greeting him, smiling at him. Perhaps he had finally mastered hiding his emotions behind a mask, that hardly ever slipped. Or perhaps his people hat become so numb, so used to seeing devastation in each other's eyes, that it didn't register anymore.
Back alone in his trusty old ship the Doctor expected his mask to shatter like it had so many times before. But there were no tears left to cry. The horror and pain had eaten away at him until there was nothing left. Behind his mask was only emptiness as black and cold as the void between the stars.
With a small sigh of regret the soldier stepped up to the controls of his TARDIS and entered the coordinates of his next battlefield.
The End