A new figure appeared in the cockpit doorway, a passenger the crew had called forward, a physician with his sleeves pushed up and his face gone grave.

He had examined the first officer, he said, and he wanted the captain to hear it from him directly.

This was not a stroke, and it was not a heart attack, and it was not any of the ordinary catastrophes a body produces on its own at altitude.

The pattern of it, the way it had come on, the specific signs the man was showing, all of it pointed somewhere else.

The first officer, the doctor said, carefully, had been poisoned.