For the first three seconds, Wolf felt panicked, and in that state he wanted to reach for the red button to kill, kill, before . . . Before what? His trained warrior’s mind took over and more calmly assessed the situation. The statistics were bull, for a start. Whenever anyone wanted to do anything dodgy, they fired a load of meaningless numbers at you. There wasn’t even any point trying to do math with statistics like that (what’s 60 percent of 50 percent?) because there was no authority behind them. Who on earth had worked them out?

Other information was missing. If the object was not an alien spaceship, then what was it? The statistics didn’t say. What if it was something that would be dangerous to bomb, like radioactive waste or a meteorite full of molten lava? And aliens might be hostile, but what if they were tiny or weak? Hostility isn’t a reason to kill something. And if they weren’t hostile? Maybe they’d have brought a cure for the common cold or a solution to world poverty. These thoughts went through Wolf’s mind so fast he didn’t quite register them all. But the main feeling he had was that killing is always wrong if there is another option. And violence is best avoided except in self-defense. Or in the direct defense of others. Would this be self-defense, or the defense of others? Wolf didn’t know. It wasn’t clear enough. He pressed the black button just as the voiceover got to “two, one . . .” He realized he was the last person to press his button. On his sheet he simply wrote: Not enough evidence.

There was another pause. This time three people were eliminated. Wolf wondered what they’d chosen. Presumably different from him, although maybe the reasoning had something to do with it. His warrior’s mind kicked in again. Don’t think about what others are doing, it said. Stay focused and calm. Trust yourself.

The next thing that came on the screen was a picture of a man with brown hair and a mustache. Then pictures of concentration camps, and hundreds of starving, desperate people. These were familiar pictures from history classes at every school Wolf had ever been to.

“This man personally ordered the deaths of millions of people,” said the voiceover. The picture now changed to one of a young boy. “This is him as a child. You have the chance to kill him, and prevent all those deaths, and a world war. Do you do it? Please note that this question has several parts and no one will be eliminated until all parts are complete.”

This time Wolf was one of the first to press his button.