“Let me show you,” said Boardman.

He spoke a command. A robot drone probe detached itself from the belly of the plane and streaked toward the city. Board-man and Rawlins followed the flight of the blunt gray metal projectile until it was only a few score meters above the tops of the buildings. Through its faceted eye they had a sharp view of the city, revealing the intricate texture of much of the stonework. Suddenly the drone probe vanished. There was a burst of incandescence, a puff of greenish smoke—and then nothing at all.

Boardman nodded. “Nothing’s changed. There’s still a protective field over the whole thing. It volatilizes anything that tries to get through.”

Now they had all seen the city from the air, and had seen what the guardians of the maze could do to a drone probe that ventured into the protective field overlying the city.

Rawlins had suggested the possibility that there might be a null spot in that protective field... they loaded a probe with metal pellets and stationed it fifty meters above the highest point of the maze. Scanner eyes recorded the action as the drone slowly turned, spewing the pellets one at a time into preselected one-meter-meter boxes above the city. Each in turn was incinerated as it fell...