The tower stood four days later, exactly as Wat had promised and grudgingly under budget on the elm. Thomas climbed the ladder himself for the first burn, mostly because Elias refused to let anyone else touch the shutter mechanism he'd spent two nights designing out of a broken chest-hinge and a square of tin.
"You count to three, you close it, you count to three again," Elias said, for perhaps the fourth time, crouched beside the small brazier at the platform's center. "Three counts is a wagon-train. If you lose count, close it anyway and start over. A confused signal is worse than no signal — it tells the man on the far hill that something is wrong here, and he has no way of knowing what."
"I can count to three, Elias."
"You are a man who once told me a device could hold every book ever written and still run out of patience explaining a hinge to me twice. I am allowed to be thorough."
Below them, the lane was empty of wagons at this hour, the wool trade having gone quiet with the light. Thomas struck the flint, fed the small fire, and watched the first thin column of smoke bend sideways in the wind before Elias cursed and adjusted the baffle. On the third try the shutter closed clean over the flame, held, opened, and the light shot out across the darkening valley in a single hard line toward the second hill.
They waited. The cold came up through the platform boards and into Thomas's boots, and for a long time there was nothing on the second hill but the ordinary dark of a hillside at dusk.
Then a light answered.
It was small and yellow and it flickered exactly three times before it steadied, and Elias made a sound Thomas had never heard out of him before — something close to a laugh, startled out of a man who didn't seem to know what to do with it once it had escaped.
"There," Elias said, and then, quieter, almost to himself, "There. Eleven years I have walked that ground on my own two feet, and it just told me a wagon had passed in less time than it takes water to boil."
Thomas said nothing. He was watching the small light on the far hill, thinking of a different kind of signal — a green line of text arriving a day late from a place he could no longer walk to either — and for once the comparison didn't sting the way it usually did. This one, at least, he'd built to answer back.
Old Joan was waiting at the foot of the ladder when they came down, wrapped in her shawl against the cold, having apparently decided the whole business was worth losing an hour of sleep over. "So," she said, looking up at the dark tower with open suspicion. "You've built the valley a second moon. Does it keep the wolves off the sheep pens, or just tell us which direction they're coming from?"
"The second one, mostly," Thomas admitted.
"Well, that's something, I suppose. My mother always said the worst part of trouble wasn't the trouble itself, it was not knowing it was coming until it was already at the door." She sniffed, unconvinced but unwilling to say so outright, and turned back toward the lane. "Don't let that fool up there fall off it playing with his hinges. Good mapmakers are harder to replace than good masons."
Elias, still catching his breath at the base of the ladder, didn't look offended. He looked, if anything, like a man who had just been paid the only compliment that mattered to him.