A/N: This is the second teaser for my upcoming series, The Enterprise and The Doctor, a crossover of the Star Trek universe with Doctor Who. The series is set within the collection named "To Boldly Go", which is my way of celebrating the 50th anniversary of Star Trek.

OBS: AU for Doctor Who since this is set on the Star Trek universe.

The doors opened with a bang and the two friends ran inside, the Doctor closing it after himself. Diana collapsed into the nearest armchair and started laughing out loud, now that the danger had passed, while he went straight to the console and activated the engine. The TARDIS dematerialized with the usual wheezing noises and the Doctor sat in the sofa, grinning, fondly watching his companion.

"Are you all right?" he asked, after a few moments, worried that Diana hasn't stopped laughing yet and her cheeks were reddening.

"Arr" she wheezed, trying to stifle the laughter, "yes, I think so... That was fun!" She looked at him, still giggling, and commented nervously "I never thought I'd get used to it, in the beginning, but now... I guess I'll miss it, all the excitement and running."

He sobered. "So it's time. Are you certain?"

"Yes, Doctor. We talked about it. You agreed."

He stood and, without saying anything, went to the central console and began setting the coordinates for their last destination together. She watched him while the ship shuddered and the rhythm of the engine changed. He was avoiding her gaze, looking down at the instruments. She stood, sighing, and began walking towards the corridor leading to her room, to pack.

Stopping suddenly, she gathered her courage and approached the human-looking alien that was now her best friend, in fact, her only remaining friend in all the universe. She shivered. Had she lost her mind, to leave him, to settle in a new place with only distant relatives to call as family? No, it had to be done, and it had to be done now, before she lost the courage again, or, worse, before she died in one of those trips. His was a very dangerous lifestyle, she had enjoyed it but it couldn't last. There was more she wanted to do with her life. Besides, she loved him enough that she didn't want him burdened by the guilt of her death. It was clearly hard for him, parting company, perhaps even harder than it was for her. His psychic shields were fully raised and she could not sense anything from him, but his blank face told her what she needed to know. He did not know how to say goodbye, so she had to say it for his sake, for both of them.

"I'll never forget you, Doctor. You saved me from the Federation. I'd be dead by now, but you gave me a new chance for life, and a reason to live."

"No, it was you who saved me, Diana."

"Well, I guess if I wasn't there, you'd have found another way to escape."

"You don't know that." he said seriously, fiddling with a dial.

'No', she thought. 'I don't know. There are too many things about you that I don't know. That's part of the problem. But I know enough, and I can guess some of the rest. There's much more to you than you let anyone know.'

"You have to promise me, you won't continue avoiding the Federation any longer", she said.

"Why not?" he retorted, petulantly, turning a switch on the console.

"You are far too old to behave like a child", she chided him. He sometimes felt old and weary, certainly much older than herself, but she had no idea exactly how old he was. He always avoided the question, as with most personal questions. "You'll have to go back sooner or later."

"There's no need to rush" he replied softly, hunched over the console, peering at one of the displays.

"You know it has to happen. It has already happened."

He finally turned towards her. "It'll happen when it has to. It's how it's always done" he said, his eyes telling her he was serious now. "It has been an immense pleasure travelling with you, Diana."

She turned her back to him and nearly ran down the corridor to her room.

When she returned with her packed luggage, he was waiting, leaning against the console, looking at her. His eyes were soft and full of affection. She had always suspected he considered her as a sort of daughter, and the way he was now looking at her, it seemed to her the way a parent would look at his child the day she left their home to live her own life. It didn't matter she was more than three Earth decades old, for him she might well be very much a child.

She noticed that they had already landed, the engine was still and there was only the soft murmur his ship always seemed to emit. She fought to stifle the tremors of fear that threatened to overcome her for a moment.

"I guess it is it, then" and kicked herself, how lamer could it be? "Er, maybe you could come to visit, later?" she said, tentatively.

He looked at her sadly. "No. You have your own life to live now. You have no need of me."

"Perhaps, you could leave a communicator with me, like the one you used that time on Argana, so I could call if I needed you." She saw that he looked pained, and wondered if he'd just turn away, but he answered instead.

"No", he said simply.

"Why not?"

"I have many enemies. If I left you with the means to contact me, they'd come after you, try to use you. I cannot. You'll be alright, don't worry."

"How would they know? I wouldn't tell anyone."

"They would know. I can't risk it" and she saw in his face that it was his final answer on the matter. "I've already done too much to mess up your life, Diana. It's your life to live, now."

"No, Doctor, if there's one thing you have to know about me, it's this. My life is much better for having met you. I'm very different from that naive, lost girl you met. If I could choose I'd do it all over again."

"I took you from your place in the Federation, you lost your job, you are wanted for treason," he replied, with a sad smile. "You can never go back to your home and friends. You have to start again here, so far away from your birthplace."

"You saved me. Doctor, I had to hide what I was, what I thought, what I wanted, it was a nightmare that would only get worse. If you hadn't happened, I'd eventually be found out. Besides, these last few years - how long has it been, by the way?"

He chuckled. "It's not easy to keep track of time in the TARDIS, is it? Some five of your years have passed." He sobered. "You've stayed longer than most of my companions, at least the human - or near human - ones."

"Ha, so you admit, you've had other companions before me!"

"I never denied it, did I?"

"No, but you never said anything about them either." He didn't reply. "Doctor, why are you so mysterious about yourself?"

"As I said, Diana, it's best that you don't know too much about me, it's dangerous - "

"It's not just that, is it, Doctor? You are too mysterious." He didn't say anything, he simply stood there. "All right, don't worry, I won't tell anyone about you."

He didn't reply, only looked at her. She couldn't resist it any longer, she ran up to him and hugged him hard. He initially stiffened but soon relaxed and reciprocated, and they stayed there a few moments, savoring the company of each other one final time. Then she released him, turned back to pick her things up and moved towards the doors, which opened on his command. She left without looking back, and only turned when she heard the doors closing. She observed as his ship left, then turned back towards the path to the city, for her next adventure.

End Notes: Second story in my collection To Boldly Go, set in the Star Trek universe. The stories will be mostly canon except perhaps for a few details. I'll be publishing a new story or chapter every Friday.
You don't need to know about Doctor Who to enjoy the series. This is the only story where it may not be true.