She was having trouble with her school project. Of all the things for him to see, the time he came back to visit before his time, it was the project that he was there for. Martha Jones, age 10, struggling with a project over the Virgin Queen.
He didn't know why he decided that his help was needed, but the next day he found himself in fourteenth century London, charming his way into the palace and the Queen's audience chamber.
Things did not go well. Somehow, between stealing the name of a lord who had recently passed and revealing the end of the latest Shakspeare play by accident, he ended up accused of slander and assault of the queen, and confined to the Tower. However, then the Queen herself decided that she didn't want the strange future-telling man executed, and came to his cell.
The next few hours were strange, to say the least. Somehow, he ended up with the Queen in a scullery maid's gown, running from the Tower and into the Thames- not the brightest idea, as the Thames was essentially the runoff of sewage and whatever else might need disposal by the average Londoner.
Somehow, the amount of sheer muck in the thrice-damned river managed to wreck the sonic, meaning the Doctor had no way to help the Queen dry when he finally managed to tug her out. Which, of course, wouldn't have meant much, because he was then immediately escorted back to the castle to wait for the Queen to clean up before managing his final sentencing.
Around that time, his younger self decided that now was the perfect time to show up outside his window. That was all he needed, and he flipped himself over the window sill and scaled the walls, making a run for it and leaving the room empty.
He heard the shouts ten minutes later as he raced through the streets for the closest TARDIS, the one his younger self had left behind. He leaped into it and closed the door just as the queen's guard appeared, screaming in fear when the box disappeared.
The Queen dismissed several dozen guards for failing to obtain the box.
He went back to the TARDIS he'd left behind, in the Queen's personal chamber, and quickly set the one his younger self and Martha had abandoned to a remote relay, sending it back where he'd found it. Couldn't leave his younger self to clean up his messes. Besides, they'd get to that after Shakespeare destroyed that damn play.
Research complete, he returned to 1995, parking the TARDIS down the road from Martha's house. He wrote up his information in short-hand Gallifreyan, and had the TARDIS translate it and bind it into a slim blue book. Then he slipped from the TARDIS and strode up the road, where he stopped, staring up at Martha's bedroom window for a long time.
Finally he swung himself up hand over hand on the trellis and slipped through her open window. Looking down at her in her bed, he realized that she'd been asleep this whole time. He hadn't been gone an hour, but in that time she'd given up on her project for the night and gone to bed. He smiled and stroked her hair back from her forehead, and watched as she sighed and rolled over in her sleep.
He glanced at the clock and shook himself- her REM cycle would reach the easily woken stage soon- and set the book on her desk for her to find the next day. Then he slipped from the window and was gone.
A/N: Not beta'ed or brit-picked, and I kind of wrote this at 3 am. I had a ton of caffeine and this is the crash.