"How does it work?"

"I don't know, not well enough to build one. At the focal point of two beams, it sets up a field in which molecules can't hold together anymore. Electrons can't be shared. How much physics do you know, at that level?"

"We spend most of our time on astrophysics, but I know enough to get the idea."

"The field spreads out in a sphere, but it gets weaker the farther it spreads. Except that where it actually runs into a lot of molecules, it gets stronger and starts over. The bigger the ship, the stronger the new field."

"So each time the field hits a ship, it sends out a new sphere--"

"And if their ships are too close together, it can set up a chain that wipes them all out. Then the field dies down, the molecules come back together, and where you had a ship, you now have a lump of dirt with a lot of iron molecules in it. No radioactivity, no mess. Just dirt. We may be able to trap them close together on the first battle, but they learn fast. They'll keep their distance from each other."

"So Dr. Device isn't a missile -- I can't shoot around corners.

"That's right. Missiles wouldn't do any good now. We learned a lot from them in the First Invasion, but they also learned from us -- how to set up the Ecstatic Shield, for instance."

"The Little Doctor penetrates the shield?"

"As if it weren't there. You can't see through the shield to aim and focus the beams, but since the generator of the Ecstatic Shield is always in the exact center, it isn't hard to figure it out."

"Why haven't I ever been trained with this?"

"You always have. We just let the computer tend to it for you. Your job is to get into a superior strategic position and choose a target. The shipboard computers are much better at aiming the Doctor than you are."

"Why is it called Dr. Device?"

"When it was developed, it was called a Molecular Detachment Device. M.D. Device."

Ender still didn't understand.

"M.D. The initials stand for Medical Doctor, too. M.D. Device, therefore Dr. Device. It was a joke." Ender didn't see what was funny about it.

They had changed the simulator. He could still control the perspective and the degree of detail, but there were no ship's controls anymore. Instead, it was a new panel of levers, and a small headset with earphones and a small microphone.

The technician who was waiting there quickly explained how to wear the headset.

"But how do I control the ships?" asked Ender.

Mazer explained. He wasn't going to control ships anymore. "You've reached the next phase of your training. You have experience in every level of strategy, but now it's time for you to concentrate on commanding an entire fleet. As you worked with toon leaders in Battle School, so now you will work with squadron leaders. You have been assigned three dozen such leaders to train. You must teach them intelligent tactics; you must learn their strengths and limitations; you must make them into a whole."

"When will they come here?"

"They're already in place in their own simulators. You will speak to them through the headset. The new levers on your control panel enable you to see from the perspective of any of your squadron leaders. This more closely duplicates the conditions you might encounter in a real battle, where you will only know what your ships can see."

"How can I work with squadron leaders I never see?"

"And why would you need to see them?"

"To know who they are, how they think--"

"You'll learn who they are and how they think from the way they work with the simulator. But even so, I think you won't be concerned. They're listening to you right now. Put on the headset so you can hear them."

Ender put on the headset.

"Salaam," said a whisper in his ears.

"Alai," said Ender.

"And me, the dwarf."

"Bean."

And Petra, and Dink; Crazy Tom, Shen, Hot Soup, Fly Molo, all the best students Ender had fought with or fought against, everyone that Ender had trusted in Battle School. "I didn't know you were here," he said, "I didn't know you were coming."

"They've been flogging us through the simulator for three months now," said Dink.

"You'll find that I'm by far the best tactician," said Petra. "Dink tries, but he has the mind of a child."

So they began working together, each squadron leader commanding individual pilots, and Ender commanding the squadron leaders. They learned many ways of working together, as the simulator forced them to try different situations. Sometimes the simulator gave them a larger fleet to work with; Ender set them up then in three or four toons that consisted of three or four squadrons each. Sometimes the simulator gave them a single starship with its twelve fighters, and he chose three squadron leaders with four fighters each.

It was pleasure; it was play. The computer-controlled enemy was none too bright, and they always won despite their mistakes, their miscommunications. But in the three weeks they practiced together, Ender came to know them very well. Dink, who deftly carried out instructions but was slow to improvise; Bean, who couldn't control large groups of ships effectively but could use only a few like a scalpel, reacting beautifully to anything the computer threw at him; Alai, who was almost as good a strategist as Ender and could be entrusted to do well with half a fleet and only vague instructions.

The better Ender knew them, the faster he could deploy them, the better he could use them. The simulator would display the situation on the screen. In that moment Ender learned for the first time what his own fleet would consist of and how the enemy fleet was deployed. It took him only a few minutes now to call for the squadron leaders that he needed, assign them to certain ships or groups of ships, and give them their assignments. Then, as the battle progressed, he would skip from one leader's point of view to another's, making suggestions and, occasionally, giving orders as the need arose. Since the others could only see their own battle perspective, he would sometimes give them orders that made no sense to them; but they, too, learned to trust Ender. If he told them to withdraw, they withdrew, knowing that either they were in an exposed position, or their withdrawal might entice the enemy into a weakened posture. They also knew that Ender trusted them to do as they judged best when he gave them no orders. If their style of fighting were not right for the situation they were placed in, Ender would not have chosen them for that assignment.

The trust was complete, the working of the fleet quick and responsive. And at the end of three weeks, Mazer showed him a replay of their most recent battle, only this time from the enemy's point of view.

"This is what he saw as you attacked. What does it remind you of? The quickness of response, for instance?"

"We look like a bugger fleet."

"You match them, Ender. You're as fast as they are. And here -- look at this."

Ender watched as all his squadrons moved at once, each responding to its own situation, all guided by Ender's overall command, but daring, improvising, feinting, attacking with an independence no bugger fleet had ever shown.

"The bugger hive-mind is very good, but it can only concentrate on a few things at once. All your squadrons can concentrate a keen intelligence on what they're doing, and what they've been assigned to do is also guided by a clever mind. So you see that you do have some advantages. Superior, though not irresistible, weaponry; comparable speed and greater available intelligence. These are your advantages. Your disadvantage is that you will always, always be outnumbered, and after each battle your enemy will learn more about you, how to fight you, and those changes will be put into effect instantly."

Ender waited for his conclusion.

"So, Ender, we will now begin your education. We have programmed the computer to simulate the kinds of situations we might expect in encounters with the enemy. We are using the movement patterns we saw in the Second Invasion. But instead of mindlessly following these same patterns, I will be controlling the enemy simulation. At first you will see easy situations that you are expected to win handily. Learn from them, because I will always be there, one step ahead of you, programming more difficult and advanced patterns into the computer so that your next battle is more difficult, so that you are pushed to the limit of your abilities."

"And beyond?"

"The time is short. You must learn as quickly as you can. When I gave myself to starship travel, just so I would still be alive when you appeared, my wife and children all died, and my grandchildren were my own age when I came back. I had nothing to say to them. I was cut off from all the people that I loved, everything I knew, living in this alien catacomb and forced to do nothing of importance but teach student after student, each one so hopeful, each one, ultimately, a weakling, a failure. I teach, I teach, but no one learns. You, too, have great promise, like so many students before you, but the seeds of failure may be in you, too. It's my job to find them, to destroy you if I can, and believe me, Ender, if you can be destroyed I can do it."

"So I'm not the first."

"No, of course you're not. But you're the last. If you don't learn, there'll be no time to find anyone else. So I have hope for you, only because you are the only one left to hope for."

"What about the others? My squadron leaders?"

"Which of them is fit to take your place?"

"Alai."

"Be honest."

Ender had no answer, then.

"I am not a happy man, Ender. Humanity does not ask us to be happy. It merely asks us to be brilliant on its behalf. Survival first, then happiness as we can manage it. So, Ender, I hope you do not bore me during your training with complaints that you are not having fun. Take what pleasure you can in the interstices of your work, but your work is first, learning is first, winning is everything because without it there is nothing. When you can give me back my dead wife, Ender, then you can complain to me about what this education costs you."

"I wasn't trying to get out of anything."

"But you will, Ender. Because I am going to grind you down to dust, if I can. I'm going to hit you with everything I can imagine, and I will have no mercy, because when you face the buggers they will think of things I can't imagine, and compassion for human beings is impossible for them."