The tower earned its keep on the ninth night, when the far light stuttered out of its ordinary rhythm — one burn, then a long pause, then three burns in quick succession, a pattern Elias hadn't taught anyone because he hadn't thought they'd need it yet.
Thomas was down in the undercroft when the boy came running with the message, and by the time he reached the gatehouse Elias was already halfway up the ladder himself, lantern swinging from one fist.
"Riders on the ridge road, moving fast, not ours," Elias called down. "Whoever's watching the second tower improvised the signal. I didn't teach them that pattern. They made it up because they needed you to know now, not by morning."
"How many?"
"The fire can't count that high. Wat's boy at the second tower can, if someone rides up to ask him." Elias was already sliding back down, boots hitting the platform boards. "Twenty minutes on a good horse. You could know before they're past the first milestone."
Twenty minutes. A year ago that would have meant nothing — riders came, riders went, and the valley found out what they wanted after the fact, the way it had always found things out. Thomas stood at the base of the tower doing the arithmetic anyway, the old reflex he couldn't turn off: twenty minutes was time enough to close the gatehouse slot, to get Victoria's ledgers out of easy reach, to have Wat's men at the wall instead of asleep in the weavers' loft.
It was also, he realized, the first time the valley had ever known trouble was coming before it arrived instead of after it had already happened.
Victoria met him at the tally-bench with her cloak still half-fastened, having heard the runner's shout from the counting room. "Alaric's men, or the Baron's?"
"We don't know yet. That's the point — we will, before they're close enough to matter."
She looked at him for a moment, and he watched her recalculate something behind her eyes, the way she did with a bad column of figures. "Then we're not defending a gatehouse anymore. We're defending three hillsides and everything between them."
"We always were. We just couldn't see it before."
The riders turned out to be Alaric's men after all — four of them, unarmored, carrying nothing more threatening than a rolled writ and a wax seal, turned back at the first milestone by Wat's night-watch before they'd gotten within sight of the keep. It was, in the end, nothing. A legal notice about grazing rights on a strip of common land nobody had grazed in a decade.
But Thomas stood on the gatehouse wall long after the all-clear had gone up the tower line, watching the small yellow light on the far ridge burn steady in the dark, and thought that the shape of the war had just changed under his feet, whether or not tonight's riders had meant anything at all.