Kenny sighed. He'd been staring down his electron microscope for nigh on four hours, and he still hadn't been able to identify the cell type. He rubbed the bridge of his nose under his glasses and leaned back in his chair. Years and years of hard work and here he was, head of the Department of Alien Zoology at U.N.I.T. with a six-figure salary … and a useless specimen.

This is hopeless. It's not even as if I can work out whether it's a plant or animal cell. The structure is animal, but the chlorophyll … it's hopeless. He pushed his glasses further up the bridge of his nose and got up out of his chair, intending to make himself a good cup of –

"Tea?"

Kenny jumped out of his skin. He whipped around hastily to come face-to-face with a man he never thought he'd see again.

"Mr. Smith?" he said incredulously.

"Doctor." Kenny blinked.

"Sorry … Doctor Smith."

"Nah, just 'Doctor'. That'll do. 'Doctor' is fine."

"Doctor … who, exactly?"

The Doctor merely smiled. Kenny looked him up and down – he was still wearing the pinstripe suit and white converse he'd worn the last time he laid eyes on him. He'd thought back then it was an odd thing for a teacher to do, but then again, he hadn't seemed like a normal teacher.

"You've not changed," Kenny said, chuckling. The Doctor looked raised an eyebrow.

"Changed my tie!" he protested mock-indignantly. Kenny laughed. The Doctor held out a mug of tea and Kenny accepted gratefully. He took a sip and found it just the right temperature to drink right away.

"Perfect," he said, indicating the tea.

"I like to think of myself as a bit of a tea connoisseur," the Doctor replied, grinning widely. Kenny sipped his tea thoughtfully.

"D'you mind if I …?" the Doctor asked, looking around.

"Help yourself," Kenny said. Like a child itching to try out a new toy, the Doctor skittered around the room, looking at microscope slides, peering through his glasses at Kenny's illegible notes, and generally making himself completely at home.

"Done alright for yourself, haven't you?" the Doctor said, sneaking a glance at Kenny. Kenny merely smiled.

"Got you to thank for that," he replied. "Them things—

"Krillitanes."

"—at school were cool, man. I mean, I knew aliens existed , but I never thought I'd be able to see them up close like that. Wanted to find out just how many different sorts there were." The Doctor grinned at him.

"You sound like me when I was your age."

"Which was when?

"Oooh … about eight hundred and fifty years ago?" He paused, considering. "Give or take a decade or two." Kenny gaped. "Oh, yeah, I'm an alien too," the Doctor added, off Kenny's look. Kenny opened his mouth to say something, then shut it again, thinking.

"Makes sense," he finally said. "It'd explain why you don't look a day older than when I last saw you."

"Which reminds me," the Doctor said, standing up suddenly and replacing his glasses. He leaned nonchalantly against the wall and fixed a friendly gaze on Kenny.

"I don't know if you noticed," the Doctor said, "but I'm a very rude bloke. Very rude. Don't particularly like it, but there it is. That's me. And I realised, the other day, that I never actually thanked you for your help that day, with the Krillitanes." He beamed at Kenny. "That was some seriously quick thinking, Kenny." Kenny shrugged modestly.

"There'd been a programme about bats on the telly the night before," he said. "Just seemed to make sense – annoy the bat people with noise and get the kids out of school."

"Two birds, one stone," the Doctor said, nodding appreciatively. "Well done. Thanks, Kenny. Thanks for helping to save the world."

Kenny shrugged again.

"It was only a fire alarm."

"Well, if you can't take a compliment …" the Doctor joked, grinning widely again. Kenny returned the smile and held out his hand for the Doctor to shake. Chuckling, they shook hands and nodded conspiratorially at each other.

"Don't s'pose I'll ever see you again?" Kenny asked.

"Maybe," the Doctor said. "You never know. You can keep the mug, by the way," he added, nodding towards Kenny's now-empty mug of tea. As the Doctor grinned at him one last time, Kenny felt as he'd done twenty years previously – so many of his questions had gone unanswered, but he felt so good at having been able to do something right that it barely mattered. He had a real sense of accomplishment about his day. After the Doctor had gone, Kenny turned his attention back to his microscope specimen, but his eye was caught by the mug the Doctor had left him. He burst out laughing when he read what was written on the mug:

I saved the world and all I got was this lousy mug.