"If it is a fast-acting gas," Burton said, "it must have high diffusibility across the lungs—"

"Or the skin," Stone said. "Mucous membranes, anything. Any porous surface."

Burton touched the plastic of his suit. "If this gas is so highly diffusible . . ."

Stone gave a slight smile. "We'll find out, soon enough."

Over the intercom, the helicopter pilot said, "Piedmont approaching, gentlemen. Please advise."

Stone said, "Circle once and give us a look at it."

The helicopter banked steeply. The two men looked out and saw the town below them. The buzzards had landed during the night, and were thickly clustered around the bodies.

"I was afraid of that," Stone said.

"They may represent a vector for infectious spread," Burton said. "Eat the meat of infected people, and carry the organisms away with them."

Stone nodded, staring out the window.

"What do we do?"

"Gas them," Stone said. He flicked on the intercom to the pilot. "Have you got the canisters?"

"Yes sir."

"Circle again; and blanket the town."

"Yes sir."

The helicopter tilted, and swung back. Soon the two men could not see the ground for the clouds of pale-blue gas.

"What is it?"

"Chlorazine," Stone said. "Highly effective, in low concentrations, on aviary metabolism. Birds have a high metabolic rate. They are creatures that consist of little more than feathers and muscle; their heartbeats are usually about one-twenty, and many species eat more than their own weight every day."

"The gas is an uncoupler?"

"Yes. It'll hit them hard."

The helicopter banked away, then hovered. The gas slowly cleared in the gentle wind, moving off to the south. Soon they could see the ground again. Hundreds of birds lay there; a few flapped their wings spastically, but most were already dead.

Stone frowned as he watched. Somewhere, in the back of his mind, he knew he had forgotten something, or ignored something. Some fact, some vital clue, that the birds provided and he must not overlook.

Over the intercom, the pilot said, "Your orders, sir?"

"Go to the center of the main street," Stone said, "and drop the rope ladder. You are to remain twenty feet above ground. Do not put down. Is that clear?"

"Yes sir."

"When we have climbed down, you are to lift off to an altitude of five hundred feet."

"Yes sir."

"Return when we signal you."

"Yes sir."

"And should anything happen to us—"

"I proceed directly to Wildfire," the pilot said, his voice dry.

"Correct."

The pilot knew what that meant. He was being paid according to the highest Air Force pay scales: he was drawing regular pay plus hazardous-duty pay, plus non-wartime special-services pay, plus mission-over-hostile-territory pay, plus bonus air-time pay. He would receive more than a thousand dollars for this day's work, and his family would receive an additional ten thousand dollars from the short-term life insurance should he not return.

There was a reason for the money: if anything happened to Burton and Stone on the ground, the pilot was ordered to fly directly to the Wildfire installation and hover thirty feet above ground until such time as the Wildfire group had determined the correct way to incinerate him, and his airplane, in midair.