She was gone.

The child had been the only link to his old home, the home where he was now a renegade, and probably forgotten by the rest of his race. He remembered how frustrated he had been in the days before he left, with the planet and the people. And yet...the Doctor had never missed the company of his own people so much.

He heard footsteps in the corridor and viciously wiped a tear away from his face. He hadn't even realised that he was crying.

Barbara entered the console room and looked at him with a concerned look on her face. The Doctor looked at her from the comfort of his chair. "What is it, Barbara?" he asked, irritably.

The young woman buried her hand in her thick, dark hair, playing with it, while she plucked up the courage to say what she had come to say. She knew the Doctor hated to be fussed over, but it was easy to see he'd been distressed since Susan had left. "Are you sure you're alright, Doctor?" she asked. "You've not been yourself since..." she trailed off, not knowing how to say the final few words without upsetting him even more.

Barbara looked into the Doctor's still, piercing eyes, expecting an explosion of some sort. To her surprise, he stood and put his hands on her shoulders, smiling. "I'm fine, Barbara, dear," he said cheerfully, "Stop worrying about me. It was time for Susan to go on her own - why would she want to stay with an old fool like me for the rest of her life? Hmm?" He stepped away from her and began tinkering with the controls of the TARDIS. Barbara noticed that his beaming smile faded as soon as he thought she had stopped watching him.

"You would tell us, though wouldn't you? If you were worried about her?" she said hesitantly.

"Of course I would, now stop making such a fuss." Barbara allowed him to shoo her out of the console room, but she was not convinced by his act at all. Susan was all he had, her and the TARDIS... Perhaps that was why he rarely strayed away from the console room anymore - maybe the machine that almost seemed to be alive at times, was helping to fill the hole Susan had left behind.

Musing on this, Barbara went into her room and tried to sleep. But it was almost impossible. She found herself thinking about her own grandfather, and how much it had hurt her when he had died. It felt like something had ripped out all her insides and then forced her to eat them.

She wondered if that was how the Doctor was feeling now. Susan wasn't dead, but he might never see her again, wouldn't be able to help her if she was in trouble.

Barbara drifted in and out of an uneasy sleep, haunted by strange feelings of despair and misery.

The Doctor, alone again, watching the central column of the TARDIS console moving up, and then down, relaxing and soothing him. He found himself thinking of his family, and of how they were, back home. He wondered how Susan was on Earth, and hoped that she was safe, knowing he couldn't protect her anymore. He wouldn't be able to comfort her if she was hurt, wouldn't be able to rescue her if she was trapped...

He told himself he had to stop thinking those thoughts, or else he'd start crying again and would fall into that bottomless pit of helplessness, where he'd come so close to falling so many times before. That was why he was so cold - because he was scared of getting too close - it hurt too much when something happened.

The Doctor had felt like this when Susan's mother had left him to get married, to a young Time Lord he didn't get on with. But it had been her life, and the Doctor had had to let her go and live it. It was exactly the same with Susan.

He tried to tell himself it was for the best - Susan had been straining for her own independence, pulling away from him for a while, even before they had left Earth with Ian and Barbara.

She had grown up so fast, and he hadn't even noticed.

He looked around the TARDIS, the home he and Susan had shared for so long, since he had run from his home planet, and had agreed to take her with him. She had been so young then, and Doctor was terrified of the responsibility, but looking back, he wouldn't have missed any of it for the world.

"You're all I've got now, girl..." he patted the wall of the TARDIS, and it seemed to purr in return. vibrating gently under his hand, its heartbeat.

Barbara had given up trying to sleep, and was exploring the TARDIS. The corridors appeared to change constantly, but she could always find her way back to the console room. She accidentally found her way there now, where the Doctor was sitting, staring into space. She backed off.

"Sorry. I lost my way. Do you want me to go?"

He shook his head. "No, Barbara, I could do with the company."

She sat beside him. "I couldn't sleep. I was thinking about my grandfather," she confessed. She felt tears welling in her eyes and she tried to swallow the lump that was rising in her throat.

The Doctor smiled sadly. "Funny, I was thinking about my granddaughter." He put his arm around her.

"Yes, I thought you might be," replied Barbara. She put her own arm round his old, but strong shoulders, and together, they sat, and watched the central column of the TARDIS moving, reminding them that somewhere, Susan was alive and happy, and in some time, Barbara's grandfather was alive and healthy. And that both of them would live on, never changing in the Doctor and Barbara's memories.