In front of him lay the "Project 5, Unit 4 Test" — a crisp, intimidating packet of eight pages. Unit 4 had been about sustainability and future energy , and Marcus had studied for three nights. He knew the difference between photovoltaic cells and passive solar heating. He could define a carbon footprint in his sleep.

As he wrote the last word, the clock hit 10:58. He closed his test booklet, feeling the strange satisfaction of solving a puzzle with his own ideas.

She winked. "That's Unit 4's real lesson."

But question four was a wall.