[Ehhh...what? He leans up into the front of the car to see what she's doing, just in case something unusual happens.]

It...uh... [No, he still can't make much sense of it. Is it better to just tell her? The story was all over the papers anyway.]

Someone who wanted revenge for a tragedy created a future London underneath the real London to fool us into thinking we'd traveled through time. This car was there.