A/N: Of course you realise that sometimes, even when you think things are finished, you find tidbits that you can include. This is a bit short, but I think it works. It's set during "Ark in Space" and "Sontaran Experiment". It starts off...well, you'll see. :)

RELATIONSHIP EXPERIMENT

The light had gone out in Sarah's eyes.

The Doctor had noticed almost as soon as he pulled her from the Ark's ventilator shaft. Even after he reassured her, when she looked up at him, the sparkle was gone. Instantly, he wondered whether he had crossed the line with his "encouragement". She still wasn't used to this new version of him, and if he honestly examined it for himself, he wasn't quite used to it either.

He looked at her sitting across the room on the floor of the cryogenic chamber. 'Well, still early days yet,' he whispered to himself.

'Did you say something?' she asked softly, but without looking up from where she was focused on the floor in front of her.

The Doctor shook his head, 'Nothing important.' He looked over at her and couldn't help but watch her as she just stared straight ahead. After a minute, he went back to examining his lash up. Even though he knew the power supply was still electrifying the chamber, it gave him something to occupy his hands as his mind continued to drift to his unusually silent companion.

As he continued to work, he talked to Sarah to try to understand what she was thinking. 'You're being awfully quiet, Sarah.'

'I don't want to disturb your work,' she replied.

'Ah, but everything's hooked up now.'

'Will it work?'

'I certainly hope so. These sleepers are depending on us. We can't let the Wirrn win.'

'Of course not.'

The Doctor frowned at the wires in front of him, then sprawled backwards into a semi-recumbent position. They each sat there, not speaking to each other, lost in their thoughts, separated by more than just the width of the room.

~!~!~!~

Sarah, for her part, stared at the floor, her exterior a calm façade belying the turmoil that was running through her mind. When she'd gotten stuck in the conduit, the Doctor had taunted and criticised her. Her previous Doctor would've never done that to her. But this Doctor was new, this Doctor she was unsure of.

When she'd seen the Doctor change faces right in front of her, it had shocked her, even though she'd seen it happen with his mentor. Then he had come to see her at her flat during the whole business with Think Tank. After the destruction of Professor Kettlewell's robot, she'd been a bit lethargic, and the Doctor and whisked her away with the promise of a change. This was not the change she'd anticipated.

She glanced over at him and watched him absently staring at various pieces of equipment that he'd hooked up. He seemed so alien to her now. Gone was the dandy of a man who easily wrapped her in a protective embrace and kissed the top of her head after her dealings with the queen spider and in his place was the aloof stranger who used belittling comments as encouragement.

She wasn't sure this was something she wanted to be a part of anymore. As she continued to ponder, another thought occurred to her. This one she put voice to. 'Either it's my imagination, or it's getting very stuffy in here.'

His response was instant, but he didn't look at her. 'It's your imagination,' he said plainly.

'You'd say that anyway,' she said softly.

~!~!~!~

Sarah's heart nearly broke when she thought the Doctor had been killed when the transport ship took off from Nerva. Harry's consolations rang hollow in her ears. All she could think was that she didn't want things between them to have ended like this. She simply shook her head in disbelief.

Then he walked through the door. It took all of Sarah's restraint not to run over and throw her arms around him. She approached him, but then thought better of it and just gently squeezed his arms instead. 'Doctor. You're safe!'

She didn't hear his response, but instead focused on the look he gave her. His eyes were intense, but behind them was a massive smile.

When he asked her to fetch him a coat from the TARDIS, she knew instantly that she was going with him, wherever that took her.

~!~!~!~

On this future, unspoilt Earth, Harry had managed to fall into a massive pit, and now Sarah looked in vain for the Doctor, finding only his sonic screwdriver. She clutched it tightly, holding onto anything that would bring her closer to the Doctor.

Finally rescuing him from the Galsec team, they head back towards the pit to look for Harry. The Doctor stopped abruptly. 'I've lost my sonic screwdriver.'

She held the device up, 'I found your sonic screwdriver, now Doctor, the pit.'

Her eyes lit up at his smile, but more so at his earnest response. 'What would I do without you?'

~!~!~!~

At that exact moment, the Doctor knew that their relationship was sure. Despite the urgency of the situation, he paused to smile as he saw the light return to Sarah's eyes.