A/N: This takes place in the same world as my story Trividian Conundrum. Without having to read all of that, the short version and what is pertinent to this is that after the Doctor dropped Sarah off in Aberdeen, she had a brief relationship with Harry Sullivan, Susan being the product of that relationship. Susan and Sarah had a rocky relationship for years, but settled into a friendly mother/daughter relationship as Susan became an adult. This story is set after Series 3 of SJA. Of course all the regular characters belong to the BBC, they just feed my imagination.

WE ARE A CONSTANT

Sarah sat at her computer in the attic, typing away on an article. After a few moments, she took off her glasses and pinched the bridge of her nose between her thumb and finger. It had been a quiet few weeks on the alien chasing front, so it gave her opportunity to get in a few freelance articles. Glancing down at her watch, she knew it was just about time for Luke to be getting home from school.

Saving her document, she turned to Mr. Smith. 'Any unusual activity, Mr. Smith?'

'No, Sarah Jane, everything is still very quiet.'

'It's nice to have some peace and quiet for a while. Let me know if you detect anything.'

As she started to leave, Mr. Smith called back out to her. 'Sarah Jane, so much for peace and quiet. I am detecting a temporal disturbance.'

Sarah quickly went to stand in front of her supercomputer. 'Where?'

'It's unstable. The first flux occurrence was approximately a half-mile away. Now it seems to be concentrated even closer.'

'Pinpoint the location as best as possible.'

After a quick moment, Mr. Smith continued. 'The occurrence is now centred right here in the attic, directly behind you.'

Sarah turned around quickly, just in time to see the TARDIS materialise. She smiled, expecting to see the young Doctor wearing the pinstriped suit and trainers emerge. Instead, the door opened, and a head emerged and looked around.

'Ah, Sarah, there you are! Perfect landing, although, the old girl had a bit of trouble homing in on you. You've moved.' He stepped out of the TARDIS and looked around, pushing his hat to the back of his head full of wild, brown curls, obviously impressed at his surroundings. 'This is very nice, Sarah, I must say.'

Sarah just stood there, eyes wide. Each time she tried to talk, no words would come out.

'C'mon Sarah, not even a "Hello" for your best friend?' He smiled, the large smile of the Cheshire cat, bright blue eyes bulging just as Sarah remembered.

She finally jolted herself into speaking. 'Doctor, it's YOU!' She looked around slowly, feeling rather lightheaded.

'Where are we, Sarah? This isn't Croydon.'

'No, we're in Ealing. I've not lived in Croydon for years. Doctor, I am surprised to see you. Or should I say, this version of you.'

The attic door opened and Luke rushed in. 'Hey Mum, I just put the kettle on.' He noticed the TARDIS instantly. Walking around the TARDIS, he recognized the tall man from some of Sarah's old pictures. 'Doctor?' he questioned.

The Doctor smiled. 'Seems you have me at a slight disadvantage, young man.'

Sarah walked over and put an arm around Luke's shoulders. 'Luke, yes, this is the Doctor, the one I did the majority of travelling with. Doctor, this is my son, Luke.'

The Doctor shook Luke's hand enthusiastically, but stared deeply into Sarah's eyes. 'Sarah, what year is this?' he asked, his velvet tones lower than she'd heard them in a long time.

'2010. February 25th.'

Looking back at Luke, he asked, 'How old are you, Luke?'

Sarah reached out and put a hand on the Doctor's arm, 'Can I talk to you for a moment?' She guided him away from Luke to another portion of the attic. 'I know what you're thinking. In my past, your future, we'll have that conversation, so I'm not having it with you now. I adopted Luke three years ago.'

The door to the attic swung open again. Susan ran in, out of breath. She pointed at the TARDIS and smiled. 'I knew it.' Then she saw the Doctor and frowned. 'Ah. Oh dear.' She pointed back towards the door. 'Bad timing, I should be going.'

As she turned to leave, Sarah called out to her in a tone she shouldn't ignore. 'Susan.' Susan turned on her heels back to face Sarah and the Doctor. Sarah just raised her eyebrows and gave her a questioning look.

'I saw the TARDIS, like it was going to materialise in front of me, but then it disappeared. Then I heard it again in the distance and figured this was the only place nearby that the Doctor would go.'

The Doctor stalked over to her. 'You're what I picked up on. How did you hear the TARDIS? You were over half a mile away from here when I landed.'

Susan pointed at her ear and grinned. 'Super hearing. Picked it up from living two years on an alien planet.'

'Timelines, Sue,' Sarah warned.

Glaring down at her, the Doctor frowned, but Susan just stood there, smiling. After a few moments, the Doctor finally spoke. 'Are you still a soldier?'

'I don't know how to be anything different.'

Sarah frowned at Susan's statement, but still said nothing as she tried to gauge the situation.

'What are you doing here?' the Doctor challenged.

'I'm not going to tell you that.'

'You are the most infuriatingly stubborn human I have ever met!' he yelled. 'And after all this time, I still don't know your name to properly yell at you.'

That's when Sarah decided to intervene. 'Excuse me, but would one of you two like to tell me what's going on?'

'I had a bit of a disagreement with one of the Colonels in UNIT and this young woman managed to stonewall me at every attempt to gather information.'

Susan rolled her eyes. 'Oi, it isn't like I knew who you were at the time. And you were after classified information. You are one of the most annoyingly condescending aliens I've ever met. And believe me, I've met several.' She finally turned to Sarah. 'When he was like this, how did you manage to travel with him as long as you did?'

The Doctor turned back to Sarah. 'Sarah, how do you know this unpleasant young woman?'

Susan looked at Sarah and saw the look in her eyes and frowned before looking back at the Doctor. She extended her hand out to the Doctor. 'Doctor, perhaps we should start over. I'm Susan. Susan Sullivan.'

Taking Susan's hand and shaking it slowly, he stared at her. 'Sullivan? Are you related to Harry Sullivan?'

Susan finally smiled. 'He's my father.'

'Well, that explains it. Harry always was an imbecile. Looks like he passed it on.' Susan shot a thought towards the Doctor, with a glare in her eyes to match. It obviously took the Doctor by surprise, as he visibility jerked his head towards her. A slow smile crossed his features. 'Oh that's very good. I take it all back, Susan,' he said as he reached out and shook her hand warmly.

Sarah stepped up. 'OK, now that the introductions are over. Luke said he'd put the kettle on. Sue, why don't you and Luke go downstairs and get the tea. The Doctor and I will be down in a minute.'

Susan nodded. 'Right Mum, c'mon Luke.'

As soon as Susan and Luke had closed the door of the attic behind them as they left, the Doctor turned back to Sarah. 'Susan just called you "Mum".'

Sarah ignored his statement and walked over and put a hand on his arm, partially just to reassure herself that he was there. 'Doctor, why are you here? I mean, this version of you. It's been over thirty years. How long has it been for you?'

The Doctor stared back at Sarah, his own blue eyes piercing into hers. 'Thirty years? I missed by thirty years?' He reached out and put his hand on her cheek, then stepped back, took off his hat and ran a hand through his curls. 'How could I have missed by that much?' He began to walk around the room and mutter to himself about his calculations and whether or not the TARDIS herself was to blame.

Sarah watched him for a minute. 'Were you trying to get back to where you dropped me off?' she asked softly.

'What? You didn't think I'd just leave you did I?' He almost sounded angry.

She frowned, staring only at the floor. 'I didn't at first.' She paused before continuing, glancing up and seeing him staring at her, she couldn't stop the tears beginning to well up. She'd already taken out her anger at her perceived abandonment on the more recent regeneration she'd met at Deffry Vale. Even though this regeneration in front of her now was the one that left her, she found that she no longer harboured any anger, only sadness at what could have been. 'I kept my ears perked up, listening for the TARDIS, jumping at shadows. But then, later, as time passed, I wasn't sure if I'd done something wrong, or if you'd died. The uncertainty tore me up inside for a long time.'

'Oh, Sarah,' his rich tones finally too much for her to bear and the tears began to flow freely. As he saw her tears, he quickly closed the distance between them and wrapped his arms around her. 'I never meant for this to happen, you have to believe me.'

Sarah pulled back slightly, but kept a tight hold on the Doctor's scarf. 'Oh, I know, but still.' She reached up and wiped away the tears. 'I promised myself that I wouldn't do this.'

'I couldn't come back right away, you understand.'

'Timelines, I know. Maintaining your history, you'll tell me a little about it someday.'

The Doctor frowned and stepped back away from her. 'So you've seen me?'

'Not this version of you, but yes, multiple times.'

He grinned. 'That's good, that's very good.' When she didn't share his smile, he continued, 'Isn't it?' He reached out and put a hand on each of her shoulders. 'I don't want details, Sarah, but I've kept my promise, haven't I? We are still a constant?' he asked.

Sarah gave a slight shrug. 'I guess that depends on what you mean by a constant.'

'You seem to have a good life here, Sarah.'

Smiling, Sarah nodded. 'It's not been typical, but then I probably would've been bored with that.' She nodded her head towards the attic door. 'Why don't you come downstairs for a minute and have a cup of tea? You'll love Luke, he saved the world the day he was born.'

Intrigued, he raised his eyebrows. 'Is he human?'

'Completely human, but grown by aliens during an invasion attempt.'

'And Susan the soldier?' He looked at Sarah and frowned. 'Harry Sullivan's child?'

Sarah sighed. 'Harry was very kind to me after you left, and we've remained very good friends over the years. Susan didn't know I was her mother until she was sixteen.'

Smiling, the Doctor draped an arm over Sarah's shoulder and steered her towards the attic door. 'Now that sounds like a story, my Sarah.'

Sarah laughed. 'It is, but it's one I can't tell you.' She relished the moment with "her" Doctor, knowing it couldn't last, no matter how much she wanted it to.

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