I was in a hurry to make up lost time when I left the quad yard, so I had gone straight to my shortcut. If the Ship were a person, the air ducts would be the circulatory system. Your blood travels from your heart to your lungs, where it passes off carbon dioxide and picks up oxygen; back to the heart; into the body, where the oxygen is used and carbon dioxide is picked up; and then back to the heart again. The air in the Ship goes through the ducts to the Third Level, where it picks up oxygen; then through the ducts and into the Ship, where the air is breathed; then back into the ducts and down to Engineers, where water and dirt, carbon dioxide, and germs are removed, and a touch of clean water is added. They kick it around a little more, and then they blow it back up to the Third Level.

The ducts moved in straight lines, and walking within them you could move through walls and arrive almost anywhere faster than you could through the halls. Anybody bigger than I was was too big to squeeze through the grate openings — there were larger openings for repairmen, but they were kept locked — and all the other kids I knew were too frightened to follow me, so the shortcut remained my own private route. They all thought I was foolish to go where I did, and for the sake of prestige I liked to pretend that they were right, though they weren’t. As long as you avoided the giant fans you were all right. It was simply that it was people, not things, that frightened me.

When I got to our corridor, I slipped the grate out and pulled myself up and out on the floor. I reset the grate and gave a swipe to my hair to teach it to behave and lie down flat again. I inherit my hair and eyes, my straight nose and my complexion from my Spanish and Indian ancestors on Daddy’s side of the family, and though I wear my black hair short, it will misbehave.