"Oooh," he said in mock-seriousness, putting up his hands. "Better not take your eyes off me, Doctor, I might whip out a tow cable and drag her away."

He sat down with the Doctor's laptop and quickly began pounding away at it. He stared at the screen intently, saying nothing for some time - though making several disapproving noises as he poured through schematics.

"...You know the fact this cobbled-together thing has even held together this long is a testament to either your engineering ability or sheer dumb luck. I'm more inclined to think the latter. In any case," he sighed as he stood up, "It's nothing serious. Your directional circuit's lost its voltage. I can repair it - or you can, if you don't trust me enough to touch your precious TARDIS."