"Sorry, lad. I've never heard of that street. Why don't you try the information robot up there?"
The information robot was a blocky green-skinned synthetic planted in a kiosk in the middle of a broad well-paved street. Alan approached and gave the robot Cavour's thirteen-century-old address.
"There is no record of any such address in the current files," the steely voice informed him.
"No. It's an old address. It dates back to at least 2570. A man named Cavour lived there."
The robot digested the new data; relays hummed softly within it as it scanned its memory banks. Finally it grunted, "Data on the address you seek has been reached."
"Fine! Where's the house?"
"The entire district was demolished during the general rebuilding of London in 2982-2997. Nothing remains."
"Oh," Alan said.
The London trail trickled out right then and there. He pursued it a little further, managed to find Cavour's name inscribed on the honor role of the impressive London Technological Institute for the year 2529, and discovered a copy of Cavour's book in the Institute Library. There was nothing else to be found. After a month in London, Alan moved on eastward across Europe.
Most of it was little like the descriptions he had read in the Valhalla's library. The trouble was that the starship's visits to Earth were always at least a decade behind, usually more. Most of the library books had come aboard when the ship had first been commissioned, far back in the year 2731. The face of Europe had almost totally altered since then.