A/N: This is a songfic of sorts, but ff . net won't let you post lyrics on here. If you haven't heard Chameleon Circuit, please listen to Nightmares before reading; it'll make things that much better. You can hear it on Spotify and YouTube.

Living in the TARDIS is like living in a vast, sprawling mansion. It has long, carpeted corridors, stairs heading every which way and lots of unexpected shortcuts. At least Donna assumes they're shortcuts – it could just be that the layout keeps rearranging itself. During her first weeks on board, she was scared to go off on her own, thinking she would likely get lost in the immense interior unless she brought a bag of bread crumbs or a ball of yarn with her. The Doctor had just grinned when she admitted that to him, told her not to worry and ushered her out of the console room.

'Live a little, Donna!' he had said. 'How else will you learn anything?'

So now, whenever they got a little downtime that she didn't need for catching up on sleep, Donna would wander around exploring. She had found many fascinating places, including a swimming pool, a huge planetarium in which you could scroll through a three-dimensional model of any solar system or galaxy, and an incredibly dusty and disused bowling alley. Just the other day on her way to bed, she had stumbled across a library. Having been to The Library, she supposed it wasn't that big, although most humans would have disagreed, but she had left off investigating it for a day when she wasn't exhausted.

That was where she was headed now, if she could remember where it was. It had had green double doors with golden door knobs… yes! There it was. Stepping through and closing the doors behind her, she started roaming along the tall mahogany bookcases which lined the walls. There were ladders leading up to a slender balcony running all the way around the room, and more ladders going up towards the skylight ceiling. Donna gaped at it, wondering how there could be a sky inside a ship that was hurtling through a time vortex. The sun was apparently setting, turning the bright sky a burnt orange. How strange that it should be sunset in the late afternoon when the TARDIS normally seemed attuned to her own country's time frame.

Strolling further in, she found a collection of instruments of various shapes and sizes. Donna had never learned to play an instrument, but she couldn't resist sitting down in front of a piano-related contraption and trying out its colourful keys. It sounded a lot like a piano as well, and she spent a few minutes trying to find the notes to Twinkle Twinkle Little Star before moving on.

There were more bookcases, only one ladder high, standing back to back in some kind of pattern across the floor. Walking slowly along a random shelf with her hand dragging across tomes and booklets in pretty bindings, she smiled to find a full collection of Agatha Christie's works. She selected Murder on the Orient Express and took it with her to a group of plush, high-backed sofas near the musical area.

Some hour-and-a-half into reading, the sky was still sunset coloured and Donna's eyelids were getting heavy. She lay down on her back and gazed up at the glass ceiling, the book open on her chest. That was no ordinary Earth sky, she thought hazily, but before she could speculate on that any further, she had dozed off.

When Donna woke up, she noticed two things: the sky had gone black, and there was music coming from behind her sofa. It sounded like the not-quite-a-piano that she had tried… seven hours ago according to her phone. How could she have slept for that long at this hour? Her book had fallen to the floor, and the library was dark around her. Just when she had picked up the book and was looking around for a lamp, the music stopped. Donna's brain suddenly kicked into gear as she realised that the only person who could be in here playing was the Doctor. She'd had no idea that he was that musical. She sat up on her knees to peer over the back of the sofa and smiled to see him in front of the large instrument. He had his back to her and was writing in a book set on the note stand. Hadn't he seen her, coming in here? She guessed not, because the only light in the room was centred around the instruments, and the sofas were sort of shielding each other. If she announced her presence, he would most likely stop playing, and she had enjoyed listening to the soothing sound of his music, so instead she lay back down on the sofa, hoping he would resume it.

When he did, she closed her eyes and let the complex notes drift through her mind. They sounded sad and contemplative now, the notes, and just a bit hesitant, as though the Doctor were just learning or composing this piece. After a while of melodies and chords weaving together, the chords were suddenly on their own and Doctor was singing the melody instead. The more Donna listened, the more she wished that she wasn't, because this song was obviously private.

[Nightmares]

After repeating the chorus, the sound of the piano turned more organ-like as he played a small melody with no accompanying chords, and then the music stopped. A few silent tears had run down Donna's temples unnoticed, and she wiped them away trying to decide what to do. She had been eavesdropping, that was all there was to it, and she felt ashamed of herself. If she could have sneaked away unseen she would have done so a while ago, but it was impossible. Then again, since she was here, couldn't she just go over there and try to take away the sadness she had heard in her friend's voice? Would he welcome her caring or would he pretend that everything was fine? She couldn't bear to see that fake smile that he plastered on his face sometimes like some kind of shield.

Several minutes of indecision passed by before Donna got worried enough by the total silence to stick her head up over the sofa back again. The Doctor was still sitting in front of his piano, but he had shut the lid and had his elbows up on it, his head in his hands. It looked like he was crying. That clinched the matter; Donna put the book down on the sofa arm and made her way over to him.

'Doctor?' she prompted, and he jumped a little, then drew his hands across his face before turning halfway around and looking up at her. His eyes held the remains of tears, but she was still relieved to see no grin on his face, just a small smile.

'Donna! I didn't hear you come in.'

'Oh, I didn't. I was asleep on the sofa,' gesturing over her shoulder towards it, 'and I just woke up.' The Doctor simply nodded, and Donna continued 'I didn't know you played the… whatever that thing is.'

'Gallifreyan melliphone. I just fool around on it sometimes, nothing grand.'

For a second, Donna considered leaving it at that, but she'd had enough of concealing things from him after the recent episode with the console room sofa and the sad tea drinking. Leaning against the melliphone and looking down at the floor, she admitted, 'I heard you singing.'

'Yeah…' the Doctor sighed, 'Sorry about that.'

'Oi, don't you apologise! I should be the one apologising for listening in. I just woke up and I heard you play and it was so beautiful, and then you started singing and I didn't know what to do. I'm sorry.' She paused, wishing he would open up or wave it all away or just say anything to break this awkwardness. When nothing was forthcoming, she asked, 'Do you often write songs in here?'

'Yeah. Well, not that often. Well… sometimes. I've always found music to be a great outlet. Feel much better now.'

'Good,' Donna said, smiling at him. And he did look a lot better, actually; less pale and red-eyed, and fairly relaxed as he smiled back. It occurred to her that he must be relieved that she wasn't pushing him to talk about the song, and maybe even glad to have her there.

'I can't play anything,' she said. 'Maybe you could teach me?'

By way of response, the Doctor scooted to one side of the long stool and patted it next to him. When she sat down, he put his arm around her shoulders briefly, squeezing, and she knew they were okay.

A/N: The melody at the end of the Doctor's song is of course The Doctor's Theme by Murray Gold, which is woven into the background of Nightmares.

Thanks for reading!