Cercy had selected Malley, the psychiatrist, because he wasn't sure that killing the Ambassador was going to be a purely physical problem.

Darrig was a mathematical physicist, but his restless, curious mind had come up with some interesting theories in other fields. He was the only one of the four who was really interested in the Ambassador as an intellectual problem.

"He's like Metal Old Man," Darrig said finally.

"What's that?"

"Haven't you ever heard the story of Metal Old Man? Well, he was a monster covered with black metal armor. He was met by Monster-Slayer, an Apache culture hero. Monster-Slayer, after many attempts, finally killed Metal Old Man."

"How did he do it?"

"Shot him in the armpit. He didn't have any armor there."

"Fine," Cercy grinned. "Ask our Ambassador to raise his arm."

"All set!" Harrison called.

"Fine. Go."

In the Ambassador's room, an invisible spray of gamma rays silently began to flood the room with deadly radiation.

But there was no Ambassador to receive them.

"That's enough," Cercy said, after a while. "That would kill a herd of elephants."

But the Ambassador stayed invisible for five hours, until some of the radioactivity had abated. Then he appeared again.

"I'm still waiting for that typewriter," he said.

"Here's the Analyzer's report." Malley handed Cercy a sheaf of papers. "This is the final formulation, boiled down."

Cercy read it aloud: "The simplest defense against any and all weapons, is to become each particular weapon."

"Great," Harrison said. "What does it mean?"

"It means," Darrig explained, "that when we attack the Ambassador with fire, he turns into fire. Shoot at him, and he turns into a bullet—until the menace is gone, and then he changes back again." He took the papers out of Cercy's hand and riffled through them.