As the Doctor and Sarah Jane ran towards the scream, they bumped into Jimmy and Olivia, who were doing the same.

''Who're you?'' Olivia questioned Sarah Jane.

''This is Sarah Jane,'' the Doctor said with a proud smile, ''She's a very old friend of mine.''

''Hi!'' Olivia beamed, shaking hands with the woman, while Jimmy smiled at her.

''Come on,'' the Doctor ordered, and they all followed him to the maths department, where they found Joshua surrounded by a load of vacum-packed rats.

''Sorry,'' Joshua said meekly, ''These fell out of the cupboards.''

''Well, as idiotic as your scream was,'' the Doctor began, eliciting a glare from Joshua, ''At least it alerted us to these... rats.''

''Isn't that a bit weird,'' Olivia noted, ''Rats in a school?''

''Well, obviously they use them in Biology lessons,'' Sarah Jane suggested, ''They dissect them.''

''Nah,'' Jimmy dismissed with a sigh, ''They don't do that anymore. And even if they did, why would they store them in the Maths department? Wouldn't they be in biology or something?''

''Everything started when Mr Finch arrived,'' the Doctor cut in, ''Let's go and check his office.'' He stalked off down another corridor.

''So how d'you know the Doc, then?'' Jimmy asked Sarah Jane.

''I used to travel with the Doctor,'' Sarah Jane replied politely.

''Oh my god,'' Olivia gushed, ''Where'd you go? What creatures did you meet? What face did he have-''

''Didn't I tell you to keep the noise down?'' the Doctor interrupted.

''Sorry,'' Olivia said, becoming quiet.

''Maybe those rats were food,'' the Doctor mused as they reached the headmaster's office, the Doctor unlocking the door with the sonic.

''Food for what?'' Olivia questioned. The Doctor peered inside, and he looked up to see a group of bat-like creatures hanging from the ceiling.

''For them.'' The group observed the giant bats for a few seconds before making a run for it.

''What the hell were those things?'' Joshua asked as the exited the school.

''Calm down, dad,'' Jimmy ordered.

''Were those the teachers?'' Olivia asked as the Doctor and Sarah Jane stepped out.

''When Finch arrived, he brought with him seven new teachers, four dinner ladies and a nurse,'' the Doctor recalled, ''That means there were thirteen of those things,'' he began to move back inside, ''I need the TARDIS. I want to analyse that oil.''

''I might be able to help you, there,'' Sarah Jane said, ''I've got something to show you!''

She led them to her car and opened the boot. She removed a blanket to reveal a robotic dog.

''K9!'' the Doctor said in awe, ''Jimmy, Olivia, this is K9 Mark 3!''

''It's a... dog,'' Jimmy noted absently.

''Well done, Jimmy, you can state the obvious,'' the Doctor mocked.

''He looks a bit beaten up,'' Joshua pointed out.

''That's a good point,'' the Doctor realised, looking at Sarah Jane, ''What happened to him?''

''Oh, one day, he just... nothing!'' Sarah Jane replied.

''You didn't try to get him fixed, did you?'' the Doctor asked, knowing that humans were not ready for that level of technology at this point in time.

''Well, it's not like getting parts for a mini-metro!'' Sarah Jane protested, ''Beside, the technology inside him could rewrite human science. I couldn't show him to anyone!''

''Right then,'' the Doctor said, picking up K9 and closing the boot, ''Let's see if an old dog's got some old tricks.''


The group went to a small chip shop not far from the school. The Doctor and Sarah Jane worked on K9 while Jimmy, Olivia and Joshua grabbed something to eat.

''I thought of you on Christmas Day,'' Sarah Jane said, ''This Christmas just gone? Great big spaceship overhead. I thought, 'Oh, yeah. Bet he's up there'.''

''I was,'' the Doctor recalled.

''And Jimmy? Olivia?''

''Jimmy was there. Olivia was... busy,'' the Doctor said, not wanting to tell her that Olivia had been on the roof.

''Did I do something wrong?'' Sarah Jane asked, ''Because you never came back for me. You just... dumped me.''

''I told you,'' the Doctor said, ''I was called back home and in those days humans weren't allowed.''

''I waited for you,'' she admitted, ''I missed you.''

''I'm not important,'' the Doctor scoffed, ''You could do just as well without me. Maybe even better.''

''You know what the most difficult thing was?'' the Doctor asked, ''Coping with what happens next, and with what doesn't happen next. You took me to the furthest reaches of the galaxy, you showed me supernovas, intergalactic battles and then you just dropped me back on Earth. How could anything compare to that?''

''What else could I do?'' the Doctor sighed.

''We get a taste of that splendour... and then we have to go back.''

''You're still investigating,'' the Doctor countered, ''You found that school. You're doing what we always did.''

''You could've come back,'' Sarah Jane said. The Doctor shook his head, ''Why not?''

''I never look back,'' the Doctor sighed, ''I can't.''

''It wasn't Croydon, where you dropped me off, it wasn't Croydon!'' Sarah Jane recalled.

''Where was it?''

''Aberdeen!''

''Oh dear,'' the Doctor murmured as K9 whirred into life, ''Hello again,'' the Doctor said to the robot dog.

''Master!'' K9 said.

''You recognise me, splendid!'' the Doctor said.

''Affirmative,'' K9 agreed.

''Olivia, oil!'' the Doctor ordered. The blonde handed over the oil.

''Don't touch it,'' she warned, ''That dinner lady got completely burnt.''

The Doctor waved her off and put his finger into the oil. He rubbed some onto the sensor that K9 had put up.

''What is it, K9?'' the Doctor asked.

''Oil. Ex- ex- ex- extract ana- an- analysing...'' K9 said, ''Confirmation of analysis - substance is Krillitane Oil.''

''Oh no,'' the Doctor murmured, ''Krillitanes.''

''Is that bad?'' Olivia asked.

''Very much so,'' the Doctor replied gravely.

''And what are... Krillitanes?'' Sarah Jane asked.

''They're a composite race,'' the Doctor explained, ''Just like your culture is a mixture of traditions from all sorts of countries, the Krillitanes are the same. An amalgam of the races they've conquered. But they take physical aspects. They cherry-pick the best bits from the people they destroy. That's why I didn't recognize them. The last time I saw them, they looked just like humans except they had really long necks.''

''What're they doing here?'' Jimmy asked.

''They want something with the children,'' the Doctor realised.

''So what's with the dog?'' Joshua asked as he and Sarah Jane put K9 back into the boot.

''The Doctor likes travelling with an entourage. Sometimes they're humans, sometimes they're aliens, and sometimes... they're tin dogs,'' she smiled at Joshua, ''What about you? Where do you fit in the picture?''

''I'm just the backup,'' the man admitted, ''Just help'em out when they need it.''

''Doctor, what're we gonna do?'' Jimmy asked as they headed out of the cafe.

''We formulate a plan of action,'' the Time Lord said, ''We find out what exactly these Krillitanes are up to and put a stop to it.'' The Doctor noticed something in the corner of his eye. It was Mr Finch, standing on the school roof with a Krillitate. Suddenly, the Krillitane swooped down over them, making them all duck, before flying off again.

''Was that a Krillitane?'' Sarah Jane asked.

''It didn't even touch us,'' Olivia noted, ''It just flew off. Why did it do that?''


The next morning, The Doctor, Olivia, Jimmy, Sarah Jane and Joshua stepped out of Sarah Jane's car as the students arrived at school.

''Jimmy, Olivia, go to the maths department with Sarah Jane. Crack open those computers, I need to see the hardware inside,'' the Doctor ordered, ''Here, you might need this,'' he handed Sarah Jane the sonic screwdriver.

''What about me?'' Joshua asked.

''Joshua, surveillance out here,'' the Doctor replied.

''What, just hang around here?''

''Here, take these,'' Sarah Jane said, handing him her car keys, ''You can keep K9 company.''

''Keep the window open a crack!'' the Doctor advised.

''He's a robot!'' Joshua protested.

''Not for him, you moron!'' the Doctor muttered, shaking his head.

''What about you?'' Jimmy asked.

''I'm going to speak to Mr Finch.''


The Doctor watched the ground floor of the school from a staircase above, making brief eye contact with Mr Finch as the headmaster walked past. He headed off in the direction Finch was going, eventually reaching the school swimming pool where Finch was waiting.

''Who are you?'' he asked.

''My name is Brother Lassa,'' Finch replied, ''And you? Clearly not a human.''

''The Doctor. Gallifreyan. Since when did Krillitanes have wings?''

''It's been our form for nearly ten generations, now,'' Finch replied, ''Our ancestors invaded Bessan. The people there had some rather lovely wings. They made a million widows in one day, just imagine.'' The Doctor looked at him in disgust.

''But you look human,'' the Doctor pointed out.

''A personal favourite, that's all,'' Finch replied, ''My brothers remain bat form. What you see is a simple morphic illusion. Scratch the surface and the true Krillitane lies beneath,'' the two began to walk towards the same side of the pool, ''And what of the Time Lords? I always thought of you as such a pompous race. Ancient, dusty senators, so frightened of change and... chaos. And of course, they're all but extinct. Only you. The last.''

''What're you planning?'' the Doctor asked, feeling his temper rising.

''You don't know,'' Finch realised,

''Why do you think I'm asking?'' the Doctor sneered.

''Well, show me how clever you are. Work it out,'' Finch taunted.

''Whatever it is,'' the Doctor rasped, ''I'm going to stop it.''

''Fascinating,'' Finch said, ''Your people were peaceful to the point of indolence. You seem to be something new. Would you declare war on us, Doctor?''

''I'd do whatever is necessary,'' the Doctor warned, getting right into Finch's face.

''But we're not even enemies,'' Finch protested, ''Soon... you will embrace us.''

''Never,'' the Doctor scoffed.

''The next time we meet, you will join with me. I promise you.''

The Doctor looked at Finch menacingly before storming out.


''It's not working,'' Sarah Jane said as she tried to get the sonic screwdriver to work.

''Let me try,'' Jimmy said, taking the device and ducking under the desk.

''So,'' Olivia said to Sarah Jane, ''What did he look like when you travelled with him?''

''When I first met him, he was tall, dashing, wore all these frilly shirts and velvet jackets,'' she recalled fondly, ''Then he changed, he was all curls, wore the longest scarf you'd ever see.'' She smiled as she remember her Doctors.

''It's still not working,'' Jimmy muttered.

''What about you two?'' Sarah Jane asked, ''What's your Doctor like?''

''Our first one talked like he was from up north,'' Olivia recalled, ''He had short hair and big ears. This one's grumpy all the time.''

''He's cool though,'' Jimmy said from below the desk.

''We'd never have spoken if it wasn't for the Doctor,'' Olivia realised.

''Are you two...'' Sarah Jane began, leaving the implication unspoken.

''NO!'' both humans exclaimed.

''Does he still stroke bits of the TARDIS?'' Sarah Jane asked Olivia mischievously.

''Oh my god, yeah he does!'' the two laughed hysterically, Jimmy chuckling under the desk.

''Any luck?'' the Doctor asked as he entered.

''Nah, Doc,'' Jimmy said, ''There's nothing.''

''All pupils to class immediately,'' the tannoy ordered, ''And would all members of staff congregate in the staff room.''

''They're putting the plan into action,'' the Doctor realised. Children approached the classroom as the Doctor worked on getting the computers open.

''No, sorry!'' Olivia said, ''This room's out of bounds.''

''Good work!'' the Doctor said to her, before looking at the computer, ''It won't open.''

''I thought the sonic screwdriver could open anything!'' Sarah Jane remarked.

''Anything except a deadlock seal. To have that level of protection means there's something inside here,'' he realised, ''What're they teaching those kids?''

Suddenly, a projection appeared across all the computers, and on the large white board at the front of the room.

''You wanted the program. There it is,'' Sarah Jane said.

''Some kind of code,'' Jimmy realised.

''Oh no,'' the Doctor muttered as he worked out what the code was, ''The Skasis Paradigm. They're trying to crack the Skasis Paradigm.''