DOCTOR: Changing history isn’t like changing a light bulb.

MEL: Why? What could happen?

DOCTOR: Well, you might burn your hand or get electrocuted or fall off a step-ladder.

MEL: In quad again. Sometimes I think I’ve seen the inside of more prison cells than I’ve had green salads.

REED: We’ve arrived at the same time as we left?

DOCTOR: Give or take an hour or so. And a couple of miles. Time travel isn’t an exact science. It’s more a vague one.

MEL: Particularly when the Doctor’s at the controls.