Richard Blade walked alone down the underground corridor two hundred feet below the Tower of London. As he walked he tried to see the corridor as would a man who'd never seen it before and knew nothing about it.

The floor was large, close-set tile, a bland, neutral brown alternating with an equally bland gray in a sort of checkerboard pattern. The tile threw up echoes from Blade's footsteps for the walls and ceiling to catch and bounce back. The floor showed signs of wear from many fast-moving feet, but it was spotlessly clean. In fact it was not merely clean, it was as antiseptic as the floor of a hospital.

So were the walls. They were not tiled, but something solid covered with pale green semi-gloss paint, easy on the eyes and easy to wash. At intervals the walls were broken by plain metal doors. All of them opened by push buttons rather than knobs, and all of them had spy eyes in the middle, so that the people inside could see anyone waiting outside. The impression the doors gave was less a hospital than a top-secret military installation. These were doors which might hide the latest guided missile or experiments with a new and deadly nerve gas.

In other places the walls were broken by metal panels with EMERGENCY stencilled on them in foot high red letters. There were no conventional fire alarms or fire extinguishers in sight, and it was impossible to guess what might lurk behind the panels.

Overhead was a ceiling of pale white acoustic tile, broken every few feet by more metal panels, ventilating grilles, squares of translucent glass or plastic, and sometimes grids of small holes that might have been made by termites. At intervals a faded discolored line ran across the floor, up one wall, across the ceiling, and down the wall again. Something once stood across the corridor in these places. Now it was gone and the corridor stretched unbroken from end to end, more than two hundred feet.