"Oh, a very old archive of information in the future," River said airily, as if it were the least interesting thing in the world. Even knowing Jack was a time-traveler like herself, she wasn't about to drop any spoilers on him about the future of Torchwood.

With a sigh and wrinkled brow, she turned off her scanner. "Either something's interfering with our search, or this should be the spot - nothing else matches the environmental conditions. We may have to do this the really old-fashioned way. I just don't understand it - it should give off a signature like it did before..."

She tugged her lips to the side. "Hang on. Do you think we could invert the heat signature and do a reverse search? I've got a theory about our circles."