It was only natural that the Doctor would appear while he was shrinking the TARDIS. The Time Lord had a bad habit of showing up at precisely the right, or wrong moment. It was almost as if he had a sixth sense about these things. Of course, being a Time Lord, it was entirely possible that he did.
"Hello Sarah Jane." the Doctor said before turning to him and giving him a glare so intense, that if looks could kill, he would've been completely vaporized before his ashes could even hit the floor.
"You'd better unshrink my TARDIS right now if you know what's good for you." the Doctor growled at him.
Giving him a rather cold look of his own, he complied with the Doctor's "request". It wasn't worth the fight that would follow if he didn't. That, and he wanted to return home to his wife and kids, and there was a good chance that wouldn't happen if he became the Doctor's enemy. Despite the fact that the Doctor generally didn't carry weapons, very few of the Doctor's enemies lived to face him twice. Sure, their species might, but the individuals themselves...The Doctor apparently kept his companions around in order to keep his hands relatively clean, much as Dumbledore had done with the Order.
"Witches." the Doctor muttered when the TARDIS was back to its usual size. "If the genetic tests hadn't come back negative, I'd swear you were all part Carrionite."
It was at that point that Sarah Jane had finally fully gotten over her shock over seeing the Doctor for the first time in decades and allowed herself to feel the anger that had been lying in wait beneath it. Storming up to the Doctor she slapped him.
"I waited for you!" she practically yelled as she started hitting him again. "I thought you'd died, and here you are..."
The Doctor had the decency to look guilty at that point, grabbing the balled fists that Sarah Jane had been repeatedly pounding into his chest. Before the Doctor could say anything to calm the woman down, a loud girlish scream echoed through the hallways. The confrontation was immediately abandoned as the Doctor ran towards the sound with him and the reporter trailing in his wake. He held his wand at the ready in case it was needed.
As they raced towards the source of the scream, they ran into a blond girl who didn't look older than twenty who was apparently the Doctor's current companion if their reactions to running into each-other were any indication.
"Who're they?" the blond asked.
"Rose, Sarah, Sarah, Rose, and that is, uh..." the Doctor said, making hasty introductions as the quartet ran down the hall towards the school kitchens.
"Harry Potter." he and Sarah Jane replied simultaneously.
"Really?" Rose practically squealed, looking at him with increased interest.
Having dealt with fans since he was eleven, he quietly pretended that hadn't happened, and let the Doctor's companion bring herself back under control. Hopefully, he wouldn't be dealing with another Ginny before she'd gotten her head screwed on straight. Most people had wondered why he'd married her considering what a fangirl she had been, but even fangirls grow up, especially when they've been thrust into the danger she had been and forced to fight, and she came with a rather large family that he wanted to be an actual part of rather than a friend of.
"For some strange reason, my companions like your biography." the Doctor said as they entered the kitchen and found a young black man who reminded him of Dean lying on the kitchen floor covered in shrink wrapped rat corpses.
As they were trying to figure out why there would be dead rats in the kitchen, well dead rats that hadn't been part of a health code violation, Sarah Jane had suggested they were there for dissection, and Rose chose to take a dig at her age while pointing out that rats weren't used for dissection anymore. He knew that look the two women shared during that particular discussion, he'd seen Audrey Weasley and Penelope Clearwater sharing the exact same look every time Penelope brought her son Richard to the Burrow. The man who'd had the rats dumped on him who was apparently named Mickey apparently recognized that look and the tension between Sarah Jane and the Doctor's new companion, there was an almost sympathetic look in his eyes as he laughed and said "Oh mate, the missus and the ex, welcome to every man's worst nightmare."
Continuing to explore the school in the dark while Sarah Jane and Rose took pot shots at each-other, they ended up at the Headmaster's office where several creatures were sleeping. Seeing as he hadn't seen anything like them either in Fantastic Beasts and where to find them or on the Being Department's roster, he figured that they were extraterrestrial, which meant he would be calling to tell Dudley that he'd found a bunch of aliens. Dudley would surely get a good laugh out of that.
After racing out of the building, looking back every few seconds to make sure they weren't being followed by the winged creatures they'd discovered, the Doctor said that they'd have to go back inside because he needed to use the TARDIS to examine some sample that Rose had gotten from the cafeteria. The Doctor glared at him when he said this, apparently still unhappy with his shrinking said TARDIS. Fortunately, they hadn't had to go back into the building with the dangerous looking winged aliens that he wouldn't try facing without a good team at his back or Ron and Hermione at the very least, because Sarah Jane had something in her car that the Doctor could use once he fixed it.
And so, they found themselves at a diner where he had one of the most uncomfortable meals of his life. The tension between Rose and Sarah Jane was almost palpable, and there wasn't a whole tribe of Weasleys there to break it up. There seemed to be a bit of tension between Mickey and the Doctor, but it was subdued, as if there was history and either one or both had mostly gotten over it. He would've been okay with that, but Sarah Jane had to go and ask the Doctor why he didn't come back.
"That's what he does!" he snapped when the Doctor refused to answer her. "He'll leave you to die, and he won't come back."
"You sound like you're speaking from personal experience." the Doctor said, examining him with interest.
"I found something out a while back, and when I went digging further I was told an interesting story about one Lily Evans. Let's just say that since you don't know me now, in the future, you're going to follow the same old pattern and leave your family behind." he said, reining in the anger that threatened to boil over and cause him to tell the man everything in detail in front of a bunch of strangers.
He briefly wondered what was so shocking about what he'd said that even the Doctor had been stunned, then he realized it was the Doctor. As Jack had once said, the Doctor doesn't do "domestics". At least he didn't until he decided to create a little nest with James Potter who had to have known that he wasn't Lily seeing as he'd gone to school with the girl for six years and had been pursuing her that entire time.